U.S. patent number 8,580,358 [Application Number 11/473,750] was granted by the patent office on 2013-11-12 for cellulose ester film, polarizing plate for in-plane-switching mode display and in-plane-switching mode display using the cellulose ester film.
This patent grant is currently assigned to Konica Minolta Opto, Inc.. The grantee listed for this patent is Shigeki Oka, Kunio Shimizu, Takashi Takebe, Koji Tasaka. Invention is credited to Shigeki Oka, Kunio Shimizu, Takashi Takebe, Koji Tasaka.
United States Patent |
8,580,358 |
Takebe , et al. |
November 12, 2013 |
Cellulose ester film, polarizing plate for in-plane-switching mode
display and in-plane-switching mode display using the cellulose
ester film
Abstract
A cellulose ester film containing a polyester represented by
Formula (1) or (2), wherein an in-plane retardation value (Ro) is 0
to 5 nm and a retardation value in a thickness direction (Rt) is
-20 to 10 nm, Ro and Rt being measured at 23.degree. C. and 55% RH:
B.sub.1-(G-A-).sub.mG-B.sub.1 Formula (1) wherein B.sub.1:
monocarboxylic acid, G: dihydric alcohol, A: dibasic acid, B.sub.1,
G and A contain no aromatic ring, m: repeat number, plural B.sub.1
may be the same or different, and plural G may be the same or
different; and B.sub.2-(A-G-).sub.nA-B.sub.2 Formula (2) wherein
B.sub.2: monoalcohol, G: dihydric alcohol, A: dibasic acid,
provided that none of B.sub.2, G and A contains an aromatic ring,
n: repeat number, plural B.sub.2 may be the same or different, and
plural G may be the same or different.
Inventors: |
Takebe; Takashi (Kawasaki,
JP), Shimizu; Kunio (Otsuki, JP), Tasaka;
Koji (Hino, JP), Oka; Shigeki (Hachioji,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Takebe; Takashi
Shimizu; Kunio
Tasaka; Koji
Oka; Shigeki |
Kawasaki
Otsuki
Hino
Hachioji |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
Konica Minolta Opto, Inc.
(Tokyo, JP)
|
Family
ID: |
37595164 |
Appl.
No.: |
11/473,750 |
Filed: |
June 23, 2006 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20070048462 A1 |
Mar 1, 2007 |
|
Foreign Application Priority Data
|
|
|
|
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Jun 29, 2005 [JP] |
|
|
2005-189682 |
|
Current U.S.
Class: |
428/1.33; 349/96;
106/139.3 |
Current CPC
Class: |
C08L
67/02 (20130101); G02B 5/3083 (20130101); C08J
5/18 (20130101); C08L 1/10 (20130101); C08L
1/14 (20130101); C08L 1/10 (20130101); C08L
2666/18 (20130101); C08L 1/14 (20130101); C08L
2666/18 (20130101); C08L 67/02 (20130101); C08L
2666/02 (20130101); C08L 67/02 (20130101); C08L
2666/26 (20130101); C08J 2301/10 (20130101); G02F
2202/40 (20130101); C08K 5/103 (20130101); G02F
1/13363 (20130101); C08L 33/10 (20130101); C09K
2323/035 (20200801); G02F 1/134363 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101) |
Field of
Search: |
;428/1.31,1.33,1.54
;106/139.3 ;349/96,122 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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04-229828 |
|
Aug 1992 |
|
JP |
|
04-258923 |
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Sep 1992 |
|
JP |
|
05-341124 |
|
Dec 1993 |
|
JP |
|
06-075116 |
|
Mar 1994 |
|
JP |
|
06-167611 |
|
Jun 1994 |
|
JP |
|
06-174920 |
|
Jun 1994 |
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JP |
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06-222213 |
|
Aug 1994 |
|
JP |
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2002-022956 |
|
Jan 2002 |
|
JP |
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2002-120244 |
|
Apr 2002 |
|
JP |
|
2003-012859 |
|
Jan 2003 |
|
JP |
|
Other References
JPO Website Machine English Translation of JP 2003-012859, Shimizu,
Jan. 15, 2003. cited by examiner .
Wikipedia, Azelaic Acid, Wikimedia Foundation, May 20, 2009. cited
by examiner .
Wikipedia, Nonanoic Acid, Wikimedia Foundation, Apr. 19, 2009.
cited by examiner .
JPO Website Machine English Translation of JP 2004-271846, Kameyama
et al. Sep. 30, 2004. cited by examiner .
JPO Website Machine English Translation of JP 2005-154764, Sasada
Yasuyuki, Jun. 16, 2005. cited by examiner .
JPO Website Machine English Translation of JP 2001-151901, Takada
et al., Jun. 5, 2001. cited by examiner.
|
Primary Examiner: Hon; Sophie
Attorney, Agent or Firm: Holtz Holtz Goodman & Chick,
PC
Claims
What is claimed is:
1. An in-plane switching mode display comprising a liquid crystal
cell and a polarizing plate on at least a viewer side of the liquid
crystal cell, the polarizing plate comprising a polarizer and a
cellulose ester film on at least one of the surfaces of the
polarizer, wherein the cellulose ester film does not contain any
compounds containing an aromatic ring and comprises a polyester
represented by Formula (1) or a polyester represented by Formula
(2), B.sub.1-(G-A-).sub.mG-B.sub.1 Formula (1) wherein B.sub.1
represents a monocarboxylic acid having 1 to 12 carbon atoms, G
represents a dihydric alcohol having 2 to 12 carbon atoms, A
represents a dibasic acid having 2 to 12 carbon atoms, provided
that none of B.sub.1, G and A contains an aromatic ring, m
represents a repeat number of 1 to 170, a plurality of B.sub.1 may
be the same or different, and a plurality of G may be the same or
different; B.sub.2-(A-G-).sub.nA-B.sub.2 Formula (2) wherein
B.sub.2 represents a monoalcohol having 1 to 12 carbon atoms, G
represents a dihydric alcohol having 2 to 12 carbon atoms, A
represents a dibasic acid having 2 to 12 carbon atoms, provided
that none of B.sub.2, G and A contains an aromatic ring, n
represents a repeat number of 1 to 170, a plurality of B.sub.2 may
be the same or different, and a plurality of G may be the same or
different, wherein (i) an in-plane retardation value of the
cellulose ester film (Ro) is 0 to 5 nm and a retardation value in a
thickness direction of the cellulose ester film (Rt) is -20 to 10
nm, Ro and Rt are represented by the following formulas,
respectively, Ro=(nx-ny).times.d Rt={(nx+ny)/2-nz}.times.d wherein
d is thickness (nm) of the film, nx is the maximum in-plane
refractive index of the film, ny is the in-plane refractive index
of the film in the direction orthogonal to the axis direction
having the maximum in-plane refraction index, and nz is the
refractive index in the thickness direction of the film, and Ro and
Rt are values measured under a condition of 23.degree. C. and 55%
RH employing a 590 nm wavelength light; (ii) a weight content of
the polyester represented by Formula (1) or the polyester
represented by Formula (2) is 2 to 30 weight % based on a weight of
the cellulose ester; (iii) a weight average molecular weight (mw)
of the polyester represented by Formula (1) or the polyester
represented by Formula (2) is not more than 20,000; (iv) a
thickness of the cellulose ester film is 20 to 80 .mu.m; and (v)
the polyester represented by Formula (1) or the polyester
represented by Formula (2) has a function to lower retardation
values Ro and Rt.
2. The in-plane switching mode display of claim 1, wherein the
weight average molecular weight (Mw) of the polyester is not more
than 10000.
3. The in-plane switching mode display of claim 1, wherein the
cellulose ester film comprises an acyl group having 2 to 4 carbon
atoms as a substituent; and the cellulose ester film meets the
following conditions: 1.8.ltoreq.SA.ltoreq.2.6
0.1.ltoreq.SP.ltoreq.1.2 wherein SA represents an acetyl
substitution degree and SP represents a propionyl substitution
degree.
4. The in-plane switching mode display of claim 1, wherein the
cellulose ester film comprises an acryl polymer.
5. The in-plane switching mode display of claim 4, wherein the
acryl polymer comprises X and Y, X representing a monomer unit
having a hydrophilic group and Y representing a monomer unit having
no hydrophilic group; a molar ratio of X:Y is 1:1 to 1:99; and a
weight content of the acryl polymer is 1 to 20 weight % base on a
weight of a cellulose ester of the cellulose ester film.
6. The in-plane switching mode display of claim 1, wherein a
thickness of the cellulose ester film is 20 to 60 .mu.m.
7. The in-plane switching mode display of claim 1, wherein the
polarizer contains an ethylenically modified polyvinyl alcohol; and
a thickness of the polarizer is 5 to 20 .mu.m.
8. A polarizing plate comprising a polarizer and a cellulose ester
film on at least one of the surfaces of the polarizer, wherein the
cellulose ester film does not contain any compounds containing an
aromatic ring and comprises a polyester represented by Formula (1)
or a polyester represented by Formula (2),
B.sub.1-(G-A-).sub.mG-B.sub.1 Formula (1) wherein B.sub.1
represents a monocarboxylic acid having 1 to 12 carbon atoms, G
represents a dihydric alcohol having 2 to 12 carbon atoms, A
represents a dibasic acid having 2 to 12 carbon atoms, provided
that none of B.sub.1, G and A contains an aromatic ring, m
represents a repeat number of 1 to 170, a plurality of B.sub.1 may
be the same or different, and a plurality of G may be the same or
different; B.sub.2-(A-G-).sub.nA-B.sub.2 Formula (2) wherein
B.sub.2 represents a monoalcohol having 1 to 12 carbon atoms, G
represents a dihydric alcohol having 2 to 12 carbon atoms, A
represents a dibasic acid having 2 to 12 carbon atoms, provided
that none of B.sub.2, G and A contains an aromatic ring, n
represents a repeat number of 1 to 170, a plurality of B.sub.2 may
be the same or different, and a plurality of G may be the same or
different, wherein (i) an in-plane retardation value of the
cellulose ester film (Ro) is 0 to 5 nm and a retardation value in a
thickness direction of the cellulose ester film (Rt) is -20 to 10
nm, Ro and Rt are represented by the following formulas,
respectively, Ro=(nx-ny).times.d Rt={(nx+ny)/2-nz}.times.d wherein
d is thickness (nm) of the film, nx is the maximum in-plane
refractive index of the film, ny is the in-plane refractive index
of the film in the direction orthogonal to the axis direction
having the maximum in-plane refraction index, and nz is the
refractive index in the thickness direction of the film, and Ro and
Rt are values measured under a condition of 23.degree. C. and 55%
RH employing a 590 nm wavelength light; (ii) a weight content of
the polyester represented by Formula (1) or of the polyester
represented by Formula (2) is 2 to 30 weight % based on a weight of
the cellulose ester; (iii) a weight average molecular weight (Mw)
of the polyester represented by Formula (1) or the polyester
represented by Formula (2) is not more than 20,000; (iv) a
thickness of the cellulose ester film is 20 to 80 .mu.m; and (v)
the polyester represented by Formula (1) or the polyester
represented by Formula (2) has a function to lower retardation
values Ro and Rt.
Description
This application is based on Japanese Patent Application No.
2005-189682 filed on Jun. 29, 2005, in Japanese Patent Office, the
entire content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a cellulose ester film, a
polarizing plate for In-Plane-Switching mode display and an
In-Plane-Switching mode display using the cellulose ester film.
BACKGROUND OF THE INVENTION
Recently, liquid crystal displays, plasma displays and organic EL
displays to be used for personal computers, word processors,
watches and desk-top calculators tend to be used in sever
conditions. Therefore, high durability is required to an optical
film such as a polarizing plate protective film, a retardation
film, a front filter for plasma display panel and a front film for
organic EL display so that the properties thereof is not
deteriorated so that, for example, the physical properties are not
degraded and the dimensional stability is maintained, in the sever
environment.
Besides, a problem of narrow viewing angle has been posed hitherto
about the liquid crystal display. Therefore, use of various kinds
of retardation film has been proposed for expanding the viewing
angle; cf. Patent Documents 1 to 5, for example. It is well known
that a cellulose ester having a lower substitution degree exhibits
a larger Rt (retardation in the thickness direction of a film)
value (refer to Patent Document 6), however, in an in-plane
switching mode liquid crystal display, desired is a cellulose ester
film having a lower Rt value, in order to enlarge a viewing
angle.
The retardation film strongly influences on the displaying
properties such as the viewing angle, color tone and the gradation
of the display. Accordingly, high dimensional stability during a
long time use and high stability in the retardation are desired to
the retardation film. Moreover, high dimensional stability of the
polarizing plate using the retardation film, particularly the
dimensional stability in the absorption axis direction of the
polarizers and superior resistivity against degradation of the
polarizing plate, are desired. The cellulose ester film disclosed
in Patent Document 7, being added with a polyester, exhibits a
superior dimensional stability, however, durability of polarizing
plate is poor. The cellulose ester film disclosed in Patent
Document 8, being added with an acryl polymer, exhibits a lowered
Rt value, however, notable deterioration of the polarizing plate
after a long time use has been observed. In order to prevent
deterioration of a polarizing plate, generally known is to add a
material containing an aromatic ring, however, addition of an
aromatic ring results in a problem in that Rt value is
increased.
When the dimensional variation during the aging for a long time is
large, stress is generated between the polarizing plate and the
adhesive or between the polarizing plate and the liquid crystal
cell pasted on the polarizing plate through an adhesive layer, and
a phenomenon so-called corner unevenness which is a white defect in
a black image is caused (refer to Patent Documents 9 and 10).
It is desirable that the retardation film not only has a function
of optical compensation for the liquid crystal cell but also is
superior as the protective film with respect to the durability of
the flatness against an environmental change. Patent Document 1:
Japanese Patent Publication Open to Public Inspection (hereafter
referred to as JP-A) No. 4-229828 Patent Document 2: JP-A No.
4-258923 Patent Document 3: JP-A No. 6-75116 Patent Document 4:
JP-A No. 6-174920 Patent Document 5: JP-A No. 6-222213
Patent Document 6: JP-A No. 2002-120244 Patent Document 7: JP-A No.
2002-22956 Patent Document 8: JP-A No. 2003-12859 Patent Document
9: JP-A No. 5-341124 Patent Document 10: JP-A No. 6-167611
SUMMARY OF THE INVENTION
The present invention has been made in view of the above mentioned
problems. An object of the present invention is to provide a
cellulose ester film exhibiting excellent dimensional stability,
anti-corner unevenness (light leaking) property, flatness, and
stability of retardation against a humidity variation; a polarizing
plate which enables excellent viewing angle stability using the
cellulose ester film; and an In-Plane-Switching mode display such
as an IPS mode and a FFS mode.
One of the aspects of the present invention to achieve the above
abject is a cellulose ester film containing a polyester represented
by Formula (1) or a polyester represented by Formula (2), wherein
an in-plane retardation value of the cellulose ester film (Ro) is 0
to 5 nm and a retardation value in a thickness direction of the
cellulose ester film (Rt) is -20 to 10 nm, Ro and Rt being measured
under a condition of 23.degree. C. and 55% RH:
B.sub.1-(G-A-).sub.mG-B.sub.1 Formula (1)
wherein B.sub.1 represents a monocarboxylic acid, G represents a
dihydric alcohol, A represents a dibasic acid, provided that none
of B.sub.1, G and A contains an aromatic ring, m represents a
repeat number, a plurality of B.sub.1 may be the same or different,
and a plurality of G may be the same or different; and
B.sub.2-(A-G-).sub.nA-B.sub.2 Formula (2) wherein B.sub.2
represents a monoalcohol, G represents a dihydric alcohol, A
represents a dibasic acid, provided that none of B.sub.2, G and A
contains an aromatic ring, n represents a repeat number, a
plurality of B.sub.2 may be the same or different, and a plurality
of G may be the same or different.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The above object of the present invention is attained by the
following structures.
(1) A cellulose ester film comprising a polyester represented by
Formula (1) or a polyester represented by Formula (2), wherein
an in-plane retardation value of the cellulose ester film (Ro) is 0
to 5 nm and a retardation value in a thickness direction of the
cellulose ester film (Rt) is -20 to 10 nm, Ro and Rt being measured
under a condition of 23.degree. C. and 55% RH:
B.sub.1-(G-A-).sub.mG-B.sub.1 Formula (1)
wherein B.sub.1 represents a monocarboxylic acid, G represents a
dihydric alcohol, A represents a dibasic acid, provided that none
of B.sub.1, G and A contains an aromatic ring, m represents a
repeat number, a plurality of B.sub.1 may be the same or different,
and a plurality of G may be the same or different; and
B.sub.2-(A-G-).sub.nA-B.sub.2 Formula (2)
wherein B.sub.2 represents a monoalcohol, G represents a dihydric
alcohol, A represents a dibasic acid, provided that none of
B.sub.2, G and A contains an aromatic ring, n represents a repeat
number, a plurality of B.sub.2 may be the same or different, and a
plurality of G may be the same or different.
(2) The cellulose ester film of Item (1), wherein
in Formula (1), B.sub.1 represents a monocarboxylic acid having 1
to 12 carbon atoms, G represents a dihydric alcohol having 2 to 12
carbon atoms, and A represents a dibasic acid having 2 to 12 carbon
atoms;
in Formula (2), B.sub.2 represents a monoalcohol having 1 to 12
carbon atoms, G represents a dihydric alcohol having 2 to 12 carbon
atoms, A represents a dibasic acid having 2 to 12 carbon atoms;
a weight content of the polyester represented by Formula (1) or of
the polyester represented by Formula (2) is 2 to 30 weight % based
on a weight of the cellulose ester; and
a weight average molecular weight (Mw) of the polyester represented
by Formula (1) or of the polyester represented by Formula (2) is
not more than 20000.
(3) The cellulose ester film of Item (2), wherein the weight
average molecular weight (Mw) of the polyester is not more than
10000.
(4) The cellulose ester film of any one of Items (1) to (3),
wherein
the cellulose ester film comprises an acyl group having 2 to 4
carbon atoms as a substituent; and
the cellulose ester film meets the following conditions:
1.8.ltoreq.SA.ltoreq.2.6 0.1.ltoreq.SP.ltoreq.1.2 wherein SA
represents an acetyl substitution degree and SP represents a
propionyl substitution degree. (5) The cellulose ester film of any
one of Items (1) to (4), wherein
the cellulose ester film comprises an acryl polymer.
(6) The cellulose ester film of Item (5), wherein
the acryl polymer comprises X and Y, X representing a monomer unit
having a hydrophilic group and Y representing a monomer unit having
no hydrophilic group;
a molar ratio of X:Y is 1:1 to 1:99; and
a weight content of the acryl polymer is 1 to 20 weight % base on a
weight of a cellulose ester of the cellulose ester film.
(7) The cellulose ester film of any one of Items (1) to (6),
wherein
a thickness of the cellulose ester film is 20 to 60 .mu.m.
(8) A polarizing plate for an in-plane switching mode display, the
polarizing plate comprising the cellulose ester film of any one of
Items (1) to (7).
(9) The polarizing plate of Item (8), wherein
the polarizing plate comprises a polarizer containing an
ethylenically modified polyvinyl alcohol; and
a thickness of the polarizer is 5 to 20 .mu.m.
(10) An in-plane switching mode display employing the polarizing
plate of Item (8) or (9).
A cellulose ester film excellent in the dimensional stability,
anti-corner unevenness (light leaking) property, flatness, and in
the stability of retardation relating to humidity variation, a
polarizing plate having high viewing angle stability using the
film, and an In-Plane-Switching type display such as IPS and FFS
can be provided by the present invention.
As a result of investigation by the inventors it was found that the
cellulose ester film excellent in the dimensional stability,
anti-corner unevenness (light leaking) property, flatness, and in
the stability of retardation relating to humidity variation can be
obtained by the cellulose ester film containing a polyester
represented by Formula (1) or (2), which has an in plane
retardation Ro of from 0 to 5 nm at an ordinary temperature and
humidity (25.degree. C., 55% RH), a retardation in the thickness
direction Rt of from -20 to 10 nm, or the cellulose ester film
containing a polyester represented by Formula (3) or (4), which has
a content of the polyester from 2 to 30% by weight, a weight
average molecular weight of not more than 10,000, a retardation in
plan Ro of from 0 to 5 nm at an ordinary temperature and humidity
(25.degree. C., 55% RH), and a retardation in the thickness
direction Rt from -20 to 10 nm.
The present invention is described in detail below.
[Polyester]
(Polyester Represented by Formula (1) or (2))
One of the characteristics of the cellulose ester film of the
present invention is to contain the polyester represented by
Formula (1) or (2).
In Formulas (1) and (2), B.sub.1 is a monocarboxylic acid
component, B.sub.2 is a monoalcohol component, G is a dihydric
alcohol component and A is a dibasic acid component; the polyester
is synthesized by these components. The components B.sub.1,
B.sub.2, G and A are each characterized in that these components
contain no aromatic ring, and m and n each represents a repeat
number.
As the carboxylic acid represented by B.sub.1, a known aliphatic or
alicyclic monocarboxylic acid can be used without any
limitation.
Though the followings can be described as examples of preferable
monocarboxylic acid, the present invention is not limited
thereto.
As the aliphatic monocarboxylic acid, an aliphatic acid having a
straight chain or a branched chain each containing from 1 to 32
carbon atoms is preferably applied. The number of the carbon atoms
is preferably from 1 to 20 and more preferably from 1 to 12. The
inclusion of acetic acid is preferable because the compatibility
with the cellulose ester is increased and mixing of acetic acid and
another monocarboxylic acid is also preferable.
Examples of preferable monocarboxylic acid include a saturated
aliphatic acid such as formic acid, acetic acid, propionic acid,
butyric acid, valeric acid, capronic acid, enanthic acid, caprylic
acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid,
undecylic acid, lauric acid, tridecylic acid, myristic acid,
pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid,
nonadecanoic acid, arachinic acid, behenic acid, lignocelic acid,
cerotic acid, heptaconic acid, montanic acid, melicic acid and
laccelic acid, and a unsaturated aliphatic acid such as undecylenic
acid, oleic acid, sorbic acid, linolic acid, linolenic acid and
arachidonic acid.
As the alcohol component represented by B.sub.2, a known alcohol
can be applied without any limitation. For example, a saturated or
unsaturated aliphatic alcohol having a straight or branched chain
containing from 1 to 32 carbon atoms can be applied. The number of
the carbon atoms is preferably from 1 to 20 and more preferably
from 1 to 12.
As the dihydric alcohol represented by G, the followings can be
cited but the present invention is not limited to them. Examples of
the dihydric alcohol include ethylene glycol, diethylene glycol,
1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol,
1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6
hexanediol, 1,5-pentylene glycol, triethylene glycol and
tetraethylene glycol. Among them, ethylene glycol, 1,2-propylene
glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene
glycol, 1,4-butylene glycol, 1,4-hexandiol, diethylene glycol and
triethylene glycol are preferable, and 3-propylene glycol,
1,4-butylene glycol, 1,6-hexanediol and diethylene glycol are
further preferably applied.
As the dibasic acid (dicarboxylic acid) represented by A, aliphatic
and alicyclic dibasic acids such as malonic acid, succinic acid,
glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic
acid, sebacic acid, undecanedicarboxylic acid and
dodecanedicarboxylic acid are preferably applicable. Particularly,
at least one selected from ones having from 4 to 12 carbon atoms is
used. Two or more kinds of the carboxylic acid may be used in
combination.
m and n each represent a repeat number which is preferably from 1
to 170.
(Polyester Represented by Formulas (3) or (4))
One of the characteristics of the cellulose ester film of the
present invention is to contain the polyester represented by
Formulas (3) or (4).
In Formulas (3) and (4), B.sub.1 is a monocrboxylic acid component,
B.sub.2 is a monoalcohol component, G is a dihydric alcohol
component having from 2 to 12 carbon atoms, and the polyester is
synthesized from them. B.sub.1, G and A each contains no aromatic
ring, and m and n each represent a repeating number.
B.sub.1 and B.sub.2 are respectively the same as B.sub.1 and
B.sub.2 defined by Formula (1) and (2), respectively.
G and A are each the alcohol component and the dibasic acid each
having from 2 to 12 carbon atoms the same as G and A in Formula (1)
or (2), respectively.
The weight average molecular weight of the polyester is preferably
not more than 20,000 and more preferably not more than 10,000. The
polyester having a weight average molecular weight of from 500 to
10,000 shows good compatibility with the cellulose ester and is not
evaporated in the film forming process.
The condensation polymerization of the polyester is carried out by
an ordinary method. For example, the polyester can be easily
synthesized by a method by directive reaction of the dibasic acid
with the glycol, a thermally melting condensation method by
polyesterization reaction or ester-exchanging reaction of the
dibasic acid or its alkyl ester such as methyl ester of the dibasic
acid with the glycol, or a method by dehydrohalogenation reaction
of a acid chloride of such the acid with the glycol. The polyester
having a weight average molecular weight not so large is preferably
synthesized by the direct reaction method. The polyester having a
molecular weight distribution rising in the low molecular weight
side shows very high compatibility with the cellulose ester so that
the cellulose ester film having low moisture permeability and high
transparency can be obtained. A known method can be applied without
any limitation for controlling the molecular weight. For example,
the molecular weight can be controlled under a suitable reacting
condition by controlling the adding amount of a mono-valent acid or
alcohol in a method for blocking the terminal of the molecular by
the mono-valent acid or the mono-valent alcohol. In such the case,
the use of the mono-valent acid is preferable from the viewpoint of
the stability of the polymer. For the acid, ones which are
difficulty distillated out from the system during the
polymerization-condensation reaction and easily distillated out
after the reaction such as acetic acid, propionic acid and butyric
acid are selected. These acids may be used in a mixed state. In the
case of the direct reaction, the molecular weight can be controlled
by stopping the reaction suitable timing according to the amount of
water distillated out from the system during the reaction.
Moreover, the control can be carried out by biasing the charging
mole number of the glycol or the dibasic acid or by controlling the
reaction temperature.
The polyester relating to the present invention is preferably
contained in the cellulose ester in a ratio of from 1 to 40% by
weight, and the polyester represented by Formula (3) or (4) is
preferably contained in a ratio of from 2 to 30%, particularly fro
5 to 15%, by weight.
A low retardation (Ro and Rt) film can be obtained by the addition
of the polyester and a polarizing plate which is low in the
degradation by high temperature and high humidity can be obtained
by the use of such the film. An In-Plane-Switching type display
which maintains high contrast and wide viewing angle for a long
time and has superior flatness can be obtained by the use of such
the polarizing plate.
It is preferable that the cellulose ester film of the present
invention further contains an acryl type polymer.
A polarizing plate considerably improved in the degradation of the
polarizer at high temperature and high moisture can be obtained by
the use of the film containing the acryl type polymer. In the
display using such the polarizing plate, the high contract is kept
for further long time and the corner unevenness is not caused
because the dimensional variation under sever conditions is
little.
In the present invention, the acryl type polymer is a polymer or a
copolymer synthesized from a monomer such as acrylic acid or
acrylate having no aromatic ring in the molecular thereof.
Examples of the acrylate monomer having no aromatic ring include
methyl acrylate, ethyl acrylate, i- or n-propyl acrylate, n-, i-,
s- or t-butyl acrylate, n-, i- or s-pentyl acrylate, n- or i-hexyl
acrylate, n- or i-heptyl acrylate, n- or i-octyl acrylate, n- or
i-nonyl acrylate, n- or i-myristyl acrylate, 2-ethylhexyl acrylate,
.epsilon.-caprolactone acrylate, 2-hydroxyethyl acrylate,
2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl
acrylate, 2-hydroxybutyl acrylate, 2-methoxyethyl acrylate and
2-ethoxyethyl acrylate, and the above-mentioned in each of which
the acrylate is replaced by methacrylate.
In the case of that the acryl type polymer is a copolymer, it is
preferable that the copolymer composed of a monomer component X
having a hydrophilic group and a monomer component Y having no
hydrophilic group and a mole ratio of X:Y is from 1:1 to 1:99.
Without this range, the degradation of the polarizer is
considerably increased when the film is used in the polarizing
plate. The content of the acryl polymer is preferably from 1 to 20%
by weight of the cellulose ester.
The acryl type polymer having a weight average molecular weight of
from 500 to 10,000 displays good compatibility with the cellulose
ester and is not volatiled during the film formation. An acryl type
polymer having an acryl type polymer as a side chain is gives
excellent transparency and extremely low moisture permeability to
the cellulose ester film when the molecular weight of such the
polymer is from 500 to 5,000. The film shows superior properties
for the polarizing plate protective film.
The above acryl type polymer can be synthesized referring the
method described in JP-A No. 2003-12859.
(Weight Average Molecular Weight)
In the present invention, the weight average molecular weight Mw of
the polyester and the acryl type polymer can be measured an
ordinary using gel permeation chromatographic GPC) method. In
concrete, the measurement was carried out by using a column of
Shodex-K806-K803, manufactured by Showa Denko Co., Ltd., at
25.degree. C., an eluate of methylene chloride, a detector of R1
and a referring sample of polystyrene. The injection amount of
sample was 100 .mu.l and the sample concentration was 0.1
weight/volume percent.
(Thin Layer Formation)
The thickness of the cellulose ester film of the present invention
may be from 10 to 200 .mu.m, and preferably from 20 to 60 .mu.m.
The variation of the retardation accompanied with the variation of
the environmental condition such as temperature is largely
inhibited by making the thickness so thin. The In-Plane-Switching
type display capable of maintaining the high contrast and wide
viewing angle under the sever conditions can be obtained by the use
of such the cellulose ester film.
(Cellulose Ester)
The cellulose ester to be used in the present invention is a
carboxylic acid ester having from 2 to 22 carbon atoms, and
preferably a lower fatty acid ester having not more than 6 carbon
atoms. For example, cellulose acetate, cellulose propionate,
cellulose butyrate, cellulose acetate phthalate, and a mixed fatty
acid ester such as cellulose acetate-propionate and cellulose
acetate-butyrate described in JP-A Nos. 10-45804 and 8-231761, and
U.S. Pat. No. 2,319,052 are usable. Among the above-mentioned,
preferable lower fatty acid ester of cellulose are cellulose
triacetate and cellulose acetate-propionate. These cellulose esters
can be used in a mixed state.
In the case of the cellulose triacetate, one having a total
acylation degree (acetylation degree) of preferably 2.7 to 3.0 and
more preferably 2.8 to 3.0 is used.
The preferable cellulose ester other than the cellulose triacetate
is ones having an acyl group containing from 2 to 4 carbon atoms as
a substituent and satisfying the following expressions I and II
wherein SA is the acetylation degree and SP is the propionyl
substitution degree. 2.8.ltoreq.SA+SP.ltoreq.3.0 Expression I
0.ltoreq.SA.ltoreq.3.0 Expression II
Examples of a preferable cellulose ester include: (SA=0.46,
SP=2.52), (SA=1.9, SP=1.0) and (SA=1.9, SP=1.08). Of these, more
preferable is an cellulose acetate propionate satisfying
1.8.ltoreq.SA.ltoreq.2.6 and 0.1.ltoreq.SP.ltoreq.1.2 (Total
acylation degree=SA+SP) is preferred. The site not substituted by
an acyl group is usually occupied by a hydroxyl group. Such the
cellulose ester can be synthesized by a known method.
The acylation degree can be determined according to the method of
ASTM-D871-96.
The number average molecular weight (Mn) of the cellulose ester to
be used in the present invention is preferably from 60,000 to
200,000, more preferably from 100,000 to 200,000, and specifically
preferably from 150,000 to 200,000.
A ratio Mw/Mn of the weight average molecular weight Mw to the
number average molecular weight Mn is preferably from 1.4 to 3.0
and more preferably from 1.7 to 2.2.
The average molecular weight and the molecular weight distribution
of the cellulose ester can be measured by a known method using high
speed liquid chromatography. The number average molecular weight,
the weight average molecular weight and the ratio of Mw/Mn can be
calculated from the measured results.
The measuring conditions are as follows.
Solvent: Methylene chloride
Column: Connected columns of Shodex K806, K805 and K803,
manufactured by Show Denko Co., Ltd.
Column temperature: 25.degree. C.
Sample concentration: 0.1% by weight
Detector: R1 Model 503, manufactured by GL Science Co., Ltd.
Pump: L6000, manufactured by Hitachi Seisakusho Co., Ltd.
Flowing rate: 1.0 ml/minute
Calibration curve: A calibration curve was used which was prepared
by using 13 standard polyethylene samples having Mw of from
1,000,000 to 500, STK Standard Polystyrene manufactured by Toso
Co., Ltd. It is preferable that the molecular weight of the every
thirteen standard samples is each about equally different from each
other in the molecular weight.
Cellulose esters synthesized from cotton linter, wood pulp or kenaf
can be used singly or in combination. Particularly, the singly or
combination use of the cellulose ester synthesized from the cotton
linter, hereinafter simply referred to as linter sometimes, or the
wood pulp is preferred.
The cellulose esters prepared from them can be used in a mixed
state in an optional ratio. These cellulose esters can be obtained
by an ordinal method using a protonic catalyst such as sulfuric
acid, an organic acid such as acetic acid and an organic solvent
such as methylene chloride when an acid anhydride such as acetic
anhydride, propionic anhydride and butyric anhydride is used as the
acylating agent.
In the case of the acetyl cellulose, the time for acetylation
should be prolonged for rising the acetylation degree. However,
excessively long time for the acetylation causes simultaneously
progress of decomposition and brings undesirable results caused by
scission of the polymer chain and the decomposition of acetyl
group. It is necessary, therefore, to set the reaction time within
a certain range for raising the acetylation degree and inhibiting
the decomposition within desired degree. It is unsuitable to
control the reaction only by the reaction time because various
conditions are applied and the reaction is largely varied depending
on the conditions such as the reaction apparatus and equipment. The
molecular weight distribution is expanded accompanied with the
progression of decomposition of the polymer. Accordingly, the
degree of the decomposition can be decided by the usually used
value of the ratio of weight average molecular weight Mw to number
average molecular weight Mn also in the case of the cellulose
ester. Namely, the ratio of Mw/Mn can be used as an indicator of
the reaction degree for carrying out acetylation reaction for
sufficient time without causing excessively decomposition by the
reaction for too long time.
An example of the production method for the cellulose ester is
described below. One hundred parts by weight of cotton linter as
the raw cellulose material was crushed and 40 parts by weight of
acetic acid was added and subjected to a pre-activation treatment
at 36.degree. C. for 20 minutes. After that, 8 parts by weight of
sulfuric acid, 260 parts by weight of acetic anhydride and 350
parts by weight of acetic acid were added to the above cotton
linter and then acetylation was carried out at 36.degree. C. for
120 minutes. The reaction system was neutralized by 11 parts by
weight of 24% aqueous solution of magnesium acetate and saponified
and ripened at 63.degree. C. for 35 minutes to obtain acetyl
cellulose. The acetyl cellulose was stirred at room temperature for
160 minutes using 10 times of an aqueous solution of acetic acid
(acetic acid:water=1:1 in weight ratio) and then filtered and
dried. Thus purified acetyl cellulose having an acetylation ratio
of 2.75 was obtained. The acetyl cellulose had a Mn of 92,000, Mw
of 156,000 and Mw/Mn of 1.7. Acetyl celluloses each having various
acetylation degrees and Mw/Mn ratios can be synthesized by varying
the acetylation conditions such as temperature, time and stirring
and that of the hydrolysis.
The synthesized cellulose ester is preferably subjected to
purification for removing low molecular weight component and to
filtration for removing un-acetylated and low-acetylated
components.
The mixed acid cellulose ester can be obtained by the method
described in JP-A No. 10-45804. The acylation degree can be
measured according to the method prescribed in ASTM-D817-9.
The cellulose ester is influenced by very small quality of metal
component contained therein. It is supposed that the presence of
the metal component is related to the water used in the production
process of the cellulose ester. The component capable of forming an
insoluble nucleus is preferably small in the amount. The amount of
a metal ion such as iron, calcium and magnesium is preferably small
because such the ion sometimes forms an insoluble substance by
foaming a slat with a polymer decomposition product having a
possibility of containing an organic acid group. The content of the
iron (Fe) component is preferably not more than 1 ppm. The
component of calcium (Ca) is much contained in ground water and
river water, and water having a high content of the calcium ion
becomes hard water, which is unsuitable for drinking water. The
calcium component tends to form a coordination compound or a
complex with an acidic component such as carboxylic acid or
sulfonic acid or many kinds of ligand and causes scum
(precipitation and turbid of insoluble compound) derived from the
insoluble calcium compound.
The amount of the calcium (ca) component is not more than 60 ppm,
and preferably from 0 to 30 ppm. The amount of the magnesium (Mg)
component is preferably from 0 to 70 ppm, and particularly
preferably from 0 to 20 ppm, because the excessive presence of the
magnesium component forms an insoluble substance. The amount of the
metal components such as iron (Fe), calcium (Ca) and magnesium (Mg)
can be measured by inductively coupled plasma-atomic emission
spectrometry (ICP-AES) after a pretreatment in which an absolutely
dried cellulose ester sample is subjected to decomposition by a
micro-digesting wet decomposition apparatus (decomposition by
sulfuric acid and nitric acid) and alkali fusion.
(Plasticizer)
A plasticizer can be further added to the cellulose ester of the
present invention.
Examples of the plasticizer which can be added to the cellulose
ester of the present invention include a phosphate type
plasticizer, a phthalate type plasticizer, a trimellitate type
plasticizer, a pyromellitate type plasticizer, a glycolate type
plasticizer, a citrate type plasticizer, a polyalcohol ester type
plasticizer and a poly-valent carboxylate ester type plasticizer,
though the plasticizer is not specifically limited. At least one
plasticizer selected from the polyalcohol ester type plasticizers
and the citrate type plasticizers can be preferably added.
The polyalcohol ester type plasticizer is a plasticizer composed of
an ester of an aliphatic polyalcohol with a mono-carboxylic acid.
An ester of an aliphatic polyalcohol having from 2 to 20 carbon
atoms is preferred.
The polyalcohol to be used in the present invention is represented
by the following Formula (3). R.sub.1--(OH).sub.n Formula (3)
In the above formula, R.sub.1 is an n-valent organic group and n is
an integer of not less than 2, OH is an alcoholic and/or a phenolic
hydroxyl group.
Examples of preferable a polyalcohol include: adonitol, arabitol,
ethylene glycol, diethylene glycol, triethylene glycol,
tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene
glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol,
1,4-butanediol, dibutylene glycol, 1,2,4-bunanetriol,
1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol,
3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane,
trimethylolethane and xylitol, but the present invention is not
limited to them. Specifically preferable are triethylene glycol,
tetraethylene glycol, dipropylene glycol, tripropylene glycol,
sorbitol, triethylol propane and xylitol.
As the monocarboxylic acid to be used in the polyalcohol ester,
specifically preferable is an aliphatic monocarboxylic acid.
Examples of the preferable monocarboxylic acid are listed below but
the present invention is not limited thereto.
As an aliphatic monocarboxylic acid, a straight or branched chain
carboxylic acid having 1 to 32 carbon atoms is preferably employed.
The number of carbon atoms is more preferably from 1 to 20, and
specifically preferably from 1 to 12. The addition of acetic acid
is preferable for raising the compatibility with the cellulose
derivative, and the mixing of acetic acid with another carboxylic
acid is also preferable.
As the preferable aliphatic monocarboxylic acid, a saturated fatty
acid such as formic acid, acetic acid, propionic acid, butyric
acid, valeric acid, caproic acid, enantic acid, caprylic acid,
pelargonic acid, capric acid, 2-ethyl-hexane carboxylic acid,
undecylic acid, lauric acid, dodecylic acid, myristic acid,
pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid,
nonadecanic acid, arachic acid, behenic acid, lignocelic acid,
cerotic acid, heptacosanic acid, montanic acid, melisic acid and
lacceric acid, and a unsaturated fatty acid such as undecylenic
acid, oleic acid, sorbic acid, linolic acid, linolenic acid and
arachidonic acid can be exemplified.
The molecular weight of the polyalcohol is preferably from 300 to
1,500, and more preferably from 350 to 750 though the molecular
weight is not specifically limited. Larger molecular weight is
preferable for low volatility and smaller molecular weight is
preferable for reducing the moisture permeability and for
increasing the compatibility with the cellulose derivative.
The carboxylic acid to be employed in the polyalcohol ester may be
one kind or a mixture of two or more kinds of them. The hydroxyl
group in the polyalcohol may be entirely esterified or may be
partially left unesterified.
Concrete compounds of the polyalcohol ester are listed below.
##STR00001## ##STR00002## ##STR00003##
Examples of a citrate plasticizer include: acetyltrimethyl citrate,
acetyltriethyl citrate and acetyltributyl citrate, although the
citrate plasticizer is not specifically limited.
The weight content of a citrate is preferably 1-30 weight % and
more preferably 2-20 weight % based on the weight of the film.
As for other plasticizers, alkylphthalylalkyl glycolates are
preferably used. Examples of an alkylphthalylalkyl glycolate
include: methylphthalylmethyl glycolate, ethylphthalylethyl
glycolate, propylphthalylpropyl glycolate, butylphthalylbutyl
glycolate, octylphthalyloctyl glycolate, methylphthalylethyl
glycolate, ethylphthalylmethyl glycolate, ethylphthalylpropyl
glycolate, methylphthalylbutyl glycolate, ethylphthalylbutyl
glycolate, butylphthalylmethyl glycolate, butylphthalylethyl
glycolate, propylphthalylbutyl glycolate, butylphthalylpropyl
glycolate, methylphthalyloctyl glycolate, ethylphthalyloctyl
glycolate, octylphthalylmethyl glycolate and octylphthalylethyl
glycolate.
Examples of a phthalate plasticizer include: diethyl phthalate,
dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate,
dibutyl phthalate, di-2-ethylhexyl phthalate and dioctyl
phthalate.
Examples of a fatty acid ester plasticizer include: butyl oleate,
methylacetyl ricinoleate and dibutyl sebacate.
Examples of a phosphate plasticizer include: triphenyl phosphate,
tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl
phosphate, diphenyl biphenyl phosphate, trioctyl phosphate and
tributyl phosphate.
(UV Absorbing Agent)
The cellulose ester film of the present invention may contain a UV
absorbing agent. The UV absorbing agent preferably exhibits a high
absorbing ability for UV rays having a wavelength of 370 nm or
less, and a low absorbing ability for visible rays having a
wavelength of 400 nm or more in view of exhibiting an excellent
visibility of a liquid crystal display.
Specific examples of a preferable UV absorbing agent used in the
present invention include: oxybenzophenone, benzotriazol, salicylic
acid ester, benzophenone, cyanoacrylate, triazine and a nickel
complex salt.
Concrete examples of a UV absorbing agent useful in the present
invention are listed below, however the present invention is not
limited thereto.
UV-1: 2-(2'-hydroxy-5'-methylphenyl)benzotriazole
UV-2: 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole
UV-3: 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole
UV-4: 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chloro
benzotriazole
UV-5: 2-(2'-hydroxy-3'-(3'',4'',5'',6''-tetrahydro
phthalimidomethyl)-5-methylphenyl)benzotriazole
UV-6: 2,2-methylenebis
(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazole-2-yl)phenol)
UV-7:
2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole
Concrete examples of a benzophenone UV absorbing agent which is one
of the useful UV absorbing agents of the present invention are
listed below, however the present invention is not limited
thereto.
U-8: 2,4-dihydroxy benzophenone
UV-9: 2,2'-dihydroxy-4-methoxy benzophenone
UV-10: 2-hydroxy-4 methoxy-5-sulfo benzophenone
UV-11: bis(2-methoxy-4-hydroxy-5-benzoylphenylmethane
Further, a compound having a 1,3,5-triazine ring is also usable as
a UV absorbing agent of the cellulose ester film of the present
invention.
Of these, a triazine compound disclosed as Formula (I) in JP-A No.
2001-235621 is also preferable to be used in the cellulose ester
film of the present invention.
The cellulose ester film of the present invention preferably
contains two or more kinds of UV absorbing agents.
As a UV absorbing agent, a polymer UV absorbing agent may also be
preferably used, and specifically a polymer type UV absorbing agent
disclosed in JP-A No. 6-148430 is preferable.
The addition methods of said UV absorbing agents are as follows.
They may be dissolved in organic solvents such as alcohol (e.g.,
methanol, ethanol or butanol), methylene chloride, methyl acetate,
acetone and dioxolane, and the resulting solution of which is added
to a dope. Alternatively, they may be added directly to a dope. UV
absorbing agents such as inorganic powder, which are not soluble in
organic solvents, may be dispersed into a mixture of organic
solvents and cellulose ester, employing a dissolver or a sand mill,
and then added to a dope.
The employed amount of UV absorbing agents may vary depending on
the type of UV absorbing agent or on the use condition, however,
the content of a UV absorbing agent is preferably 0.1-4.0% by
weight, and more preferably 0.6-2.0% by weight based on the weight
of the cellulose ester film.
<Particles>
The cellulose ester film of the present invention preferably
contains particles.
As for the particles use in the present invention, examples of
inorganic particles include: silicon dioxide particles, titanium
dioxide particles, aluminium oxide particles, zirconium oxide
particles, calcium carbonate particles, talc particles, clay
particles, calcinated caolin particles, calcinated calcium silicate
particles, hydration calcium silicate particles, aluminium silicate
particles, magnesium silicate particles, and calcium phosphate
particles. Particles containing silicon are preferable, because low
turbidity of the film is obtained. Silicon dioxide particles are
specifically preferable.
The mean diameter of primary particles is preferably from 1 to 200
nm, more preferably 5 to 50 nm, and specifically preferably from 7
to 20 nm. The particle should preferably exist as an aggregated
secondary particle of a diameter from 0.05 to 0.3 .mu.m. The
content of the particle in a cellulose ester film is preferably
from 0.01 to 1% by weight, and is more preferably from 0.1 to 0.5%
by weight. In a multi-layered cellulose ester film prepared by a
co-casting method, the particles are preferably incorporated in the
surface layer.
Particles of silicon dioxide available on the market include, for
example: AEROSIL R972, R927V, R974, R812, 200, 200V, 300, R202,
OX50 and TT600 which are manufacture by Nippon Aerosil Co.,
Ltd.
Particles of zirconium oxide available on the market include, for
example: AEROSIL R976 and R811 manufacture by Nippon Aerosil Co.,
Ltd.
Particles of polymer available on the market include, for example:
silicone resin, fluorine-contained resin and acryl resin. Among
these, silicone resin, especially three dimensionally networked
silicone resin is preferably used. Examples of silicone resins
include: TOSPERL 103, 105, 108, 120, 145, 3120 and 240, which are
manufactured by Toshiba Silicone Co., Ltd.
Among the particles listed above, AEROSIL 200V and AEROSIL R972V
are specifically preferable with respect to exhibiting a lower
friction coefficient while the low turbidity is maintained.
<Dye>
In order to optimize color of the cellulose ester film, dyes may
preferably be added. For example, a blue dye may be added to reduce
a yellow hue of the film. Preferable are anthraquinone type
dyes.
The anthraquinone type dye may have any of several kinds of
substituents in any of the 8 positions of anthraquinone. Examples
of preferable substituents include an anilino group, a hydroxyl
group, an amino group, a nitro group and a hydrogen atom. Blue dyes
disclosed in JP-A 2001-154017, specifically, anthraquinone dyes,
are preferably added to the film.
Additives described above may be added to a dope containing
cellulose ester via batch mixing, or, alternatively, they may be
added via in-line mixing using a dissolving solvent of the
additives.
In an in-line mixing process of additive solutions, a smaller
amount of cellulose ester is preferably dissolved in the dope in
order to obtain a sufficiently mixed dope. The amount of cellulose
ester is preferably from 1 to 10 weight parts in 100 weight parts
of solvent, and more preferably from 3 to 5 weight parts.
As a mixer for in-line addition and mixing, for example, a static
mixer manufactured by Toray Engineering Co., Ltd. or a static type
in-line mixer High-Mixer SWJ manufactured by Toray Engineering Co.,
Ltd., is preferably used.
<Manufacturing Method of Cellulose Ester Film>
The manufacturing method of the cellulose ester film of the present
invention will now be explained.
The manufacturing method of the cellulose ester film of the present
invention contains the processes of: a dope preparing process in
which cellulose ester and an additive, for example, above mentioned
plasticizer, are dissolved in a solvent; a casting process in which
a dope is cast on an endless metal support inventively running; a
drying process in which a cast dope is dried to form a web; a
peeling process in which a dried web is peeled from the metal
support; a stretching process or a width keeping process; a further
drying process; and a winding process of the completed film.
The dope preparation process will now be explained. In the dope
preparation process, a higher content of cellulose ester in the
dope is preferable since duration of the drying process following
the casting process is shortened, however, a too high content may
result in loss of filtration accuracy due to an increased
filtration load. Preferable content of cellulose ester is from
10-35% by weight and more preferably from 15-25% by weight.
A solvent may be used alone, however, two or more solvents may also
be used together. A mixture of a good solvent and a poor solvent is
more preferably used to increase manufacturing efficiency. A mixed
solvent being rich in a good solvent is preferable to increase
solubility of cellulose ester. The preferable mixing ratios are
from 60 to 98 percent by weight of a good solvent, and from 2 to 40
percent of a poor solvent. Herein, a good solvent is described as
being capable of dissolving cellulose ester with a single use, and
a poor solvent as being incapable of dissolving nor swelling
cellulose ester alone. Sometimes, a solvent works as a good solvent
of a cellulose ester, and sometimes as a poor solvent depending on
the average acetylation degree (degree of acetyl substitution) of
the cellulose ester. For example, acetone is a good solvent for an
acetic ester of cellulose of which the acetylation degree is 2.4,
as well as for cellulose acetatepropionate, however, it is a poor
solvent for cellulose acetate of which acetylation degree is
2.8.
Example of good solvents used in the present invention include: an
organic halide (such as methylene chloride), dioxolane, acetone,
methyl acetate and methyl acetoacetate, of these, methylene
chloride and methyl acetate are specifically preferable. However,
the present invention is not specifically limited thereto.
Examples of poor solvents used in the present invention include:
methanol, ethanol, n-butanol, cyclohexane and cyclohexanone,
however, the present invention is not specifically limited
thereto.
Example of a preferable solvent content include: 80-95 weight % of
methylene chloride and 5-20 weight % of methanol; and 60-95 weight
% of methyl acetate and 5-40 weight % of ethanol. A dope may
preferably contain 0.01-2 weight % of water.
In the process of preparing a dope, cellulose ester is dissolved
using a common method. Dissolving cellulose ester at a higher
temperature is possible when the heating is carried out under a
higher pressure. Formation of a gel or an insoluble agglomerate
(known as "Mamako" in Japanese which represents insoluble residue
when powder is dissolved in a solvent) may be avoided when the
dissolving temperature is higher than the ambient pressure boiling
point of the mixed solvents, and simultaneously the temperature is
in the range where the mixed solvents do not boil under the applied
higher pressure. The following dissolving method is also
preferable, in which cellulose ester is swollen in a mixture of
good and poor solvents followed by adding good solvents to dissolve
the swollen cellulose ester.
Pressure may be applied by injecting an inert gas such as nitrogen
or by increasing the vapor pressure of the solvents by heating.
Heating is preferably carried out from the outside of the
container. A jacket type heater is preferable because the
temperature is easily controlled.
A higher dissolving temperature is preferable with respect to the
solubility of the cellulose ester, however, too high a temperature
may lower the productivity because the pressure also becomes very
high. The dissolving temperature is preferably 45-120.degree. C.,
more preferably 60-110.degree. C. and still more preferably
70-105.degree. C. The pressure should be controlled not to allow
boiling at the set temperature.
A low temperature dissolution method is also preferably utilized,
by which cellulose ester is successfully dissolved in a solvent
such as methyl acetate.
In the next process, the cellulose ester solution thus prepared is
filtered using an appropriate filter material. A filter material
with a smaller absolute filtration accuracy is more preferable for
removing insoluble materials, however, too small a filtration
accuracy easily cause clogging up of the filter. The absolute
filtration accuracy of the filter is preferably not larger than
0.008 mm, more preferably 0.001-0.008 mm and still more preferably
0.003-0.006 mm.
The filter material used in the present invention is not
specifically limited, and plastic filters (such as polypropylene
and Teflon.RTM.) as well as metal (alloy) filters (such as
stainless steel) are preferable, since these materials are free
from peeling of a fiber, which may occur when fibrous material is
used. Impurities and, specifically, luminescent foreign materials
contained in the cellulose ester are preferably diminished or
entirely removed by filtering.
"Luminescent foreign materials" denote impurities which are
observed as bright spots when a cellulose ester film is placed
between two polarizing plates arranged in a crossed Nicols state,
illuminated with a light from one side and observed from the other
side. The number of luminescent foreign materials of larger than
0.01 mm in diameter is preferably less than 200 per cm.sup.2, more
preferably less than 100 per cm.sup.2 and still more preferably
from 0 to 10 per cm.sup.2. The number of luminescent foreign
materials of less than 0.01 mm in diameter is preferably
minimal.
The dope may be filtered by any common method. One of these
preferable filtering methods is to filter the dope at temperatures
which are higher than the ambient pressure boiling point of the
mixed solvents, and simultaneously in the range where the mixed
solvents do not boil under a higher pressure. This method is
preferable because the pressure difference between before and after
filtering (also referred to as a pressure difference) is reduced.
The filtering temperature is preferably from 45 to 120.degree. C.,
more preferably from 45 to 70.degree. C. and still more preferably
from 45 to 55.degree. C.
The pressure applied during filtering is preferably low, being
preferably not more than 1.6 Mpa, more preferably not more than 1.2
MPa and still more preferably not more than 1.0 MPa.
Casting of a dope will be explained below:
A metal support polished to a mirror finished surface is used in
the flow-casting process. A polished stainless steel belt or a
plated cast drum is used as a metal support. The width of the
support is preferably from 1 to 4 m. The surface temperature of the
metal support is preferably from -50.degree. C. to a temperature
just below the boiling point of the solvent. A relatively high
temperature of the support is more preferable because the web is
more quickly dried, however, too high a temperature may cause
foaming or loss of flatness of the web. The temperature of the
support depends on the solvent, however, is preferably in the range
of 0-70.degree. C., and more preferably 5-40.degree. C. Another
preferable method is that a web is gelated by cooling the drum
followed by peeling the web from the drum while the web still
contains much solvent. The method to control the temperature of the
support is not specifically limited and a method of blowing warm or
cool air onto the support or to apply warm water on the rear side
of the support is acceptable. The warm water method is more
preferable because the temperature of the metal support becomes
stable in a shorter time due to more efficient thermal conduction.
In the case when warm air is used, an air temperature higher than
the desired temperature is sometimes used.
In order to obtain a cellulose ester film with a sufficient
flatness, the residual solvent content of the web when it is peeled
from a metal support is preferably 10-150% by weight, however, it
is more preferably 20-40% by weight or 60-130% by weight. The
residual solvent content is specifically more preferably 20-30% by
weight or 70-120% by weight.
The residual solvent content of the web is defined by the following
formula: Residual solvent content(% by weight)={(M-N)/N}.times.100
where M represents the weight of a sample of the web collected in
the manufacturing process or after manufacturing, and N represents
the weight of the same sample after it was dried at 115.degree. C.
for 1 hour.
In the drying process of a cellulose ester film, the film is peeled
from the support and further dried until the residual solvent
decreases below not more than 1 weight %, more preferably not more
than 0.1 weight %, specifically preferably 0-0.01 weight %.
In this process, preferable is to simultaneously use the above
tenter method and a roll drying method in which a cellulose ester
film is passed through many rollers placed alternatively up and
down in a staggered manner. The method to dry the web is not
specifically limited, however, generally, hot air, IR rays or
heated rollers, for example. Hot air is preferably used with
respect to low cost. The preferable drying temperature of a web is
from 40 to 180.degree. C. The temperature is preferably increased
stepwise. In to obtain the effect of the present invention, a
higher drying temperature is preferable and the drying temperature
of 100 to 150.degree. C. is specifically preferable to obtain an
improved dimensional stability.
The cellulose ester film of the present invention is preferably
stretched in a ratio of 1.00 to 2 at least in one direction. It is
specifically preferable that the film is stretched in the film
transport direction (the longitudinal direction) just after peeled
from the support while containing much residual solvent, followed
by stretching in the width direction (the lateral direction) by
clipping both edges of the film in a tenter (biaxial
stretching).
The stretch ratios in both the longitudinal direction and the
lateral direction of the film are preferably in the range of 1.01
to 1.5, more preferably 1.02 to 1.3 and specifically preferably
1.01 to 1.1.
A stretch ratio of 1.01 to 1.3 is preferable because an excellent
flatness and a lower haze are obtained.
A film is preferably peeled from the support with a tension of not
less than 210 N/m and more preferably with a tension of 220 to 300
N/m in order to stretch the film in the longitudinal direction just
after peeled.
The cellulose ester film of the present invention is preferably a
long roll film with a length of 1000 to 6000 m. The width of the
film is preferably 1.4 to 4 m. The film preferably has areas on
both edges of the film which are subjected to a knurling treatment
of which height is 10 to 25% of the thickness of the film.
<Properties>
Moisture permeability of the cellulose ester film of the present
invention at 40.degree. C., 90% RH is preferably not more than 850
g/m.sup.224 h, more preferably from 20 to 800 g/m.sup.224 h and
specifically preferably from 20 to 750 g/m.sup.224 h. Moisture
permeability is determined employing the method prescribed in JIS Z
0208.
The elongation at break of a cellulose ester film of the present
invention is preferably from 10 to 80 percent and more preferably
from 20 to 50 percent.
The visible-light transmittance of a cellulose ester film of the
present invention is preferably not less than 90 percent and more
preferably not less than 93 percent.
Haze of the cellulose ester film in the present invention is
preferably less than 1 percent and more preferably from 0 to 0.1
percent.
The elastic modulus of the cellulose ester film of the present
invention is preferably 3000-6000 MPa.
The weight change of the cellulose ester film of the present
invention after heat treated at 60.degree. C. under 90% RH for 500
hours is preferably less than 1%.
The in-plane retardation value (Ro) of the cellulose ester film of
the present invention is 0 to 5 nm and the retardation value in the
thickness direction (Rt) is -20 to 10 nm at the condition of
ambient temperature and ambient humidity (23.degree. C. and 55%
RH).
Retardation values (Ro) and (Rt) are represented by the following
formulae. Ro=(nx-ny).times.d Rt=((nx+ny)/2-nz).times.d wherein d is
thickness (nm) of the film, nx is the maximum in-plane refractive
index of the film (also referred to as the refractive index in the
slow axis direction), ny is the in-plane refractive index of the
film in the direction orthogonal to the slow axis direction and nz
is the refractive index in the thickness direction of the film.
Retardation values Ro and Rt are determined by means of an
automatic birefringence meter, for example, KOBRA-21ADH
(manufactured by Oji Scientific Instruments) at 23.degree. C. and
under 55% RH employing a 590 nm wavelength light.
The slow axis preferably exists within .+-.10 of the lateral
direction or within .+-.1.degree. of the longitudinal direction of
the film.
The cellulose ester film of the present invention is preferably
employed as a polarizing plate protective film. The polarizing
plate protective film is preferably provided on the observation
side of the polarizing plate and, on at least one surface, a
functional layer, for example, described below is preferably
provided.
The transparent protective film (the polarizing plate protective
film) to be used in the present invention is preferably provided
with a hard coat layer as a functional layer.
The hard coat layer of the present invention is provided on at
least one surface of a polarizing plate protective film. The
polarizing plate protective film of the present invention
preferably has antireflection layers (a high refractive index layer
and a low refractive index layer) on the lard coat layer to form an
anti-reflection film.
An actinic ray curable resin layer is preferably used as the hard
coat layer.
The actinic ray curable resin layer refers to a layer which
contains, as a main component, a resin cured through a crosslinking
reaction when exposed to actinic rays such as UV light or electron
beams. The actinic ray curable resin layer preferably contains an
ethylenically unsaturated monomer, which is exposed to actinic rays
such as UV light or electron beams and cured to form a hard coat
layer. Listed as representative actinic ray curable resins are UV
curable resins as well as electron beam curable resins. The actinic
ray curable resin is preferably a UV curable resin.
Listed as UV curable resins may be, for example, UV curable
urethane acrylate resins, UV curable polyester acrylate resins, UV
curable epoxy acrylate resins, UV curable polyol acrylate resins,
or UV curable epoxy resins.
The UV curable urethane acrylate resins are easily prepared in such
a manner that acrylate based monomers having a hydroxyl group such
as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate
(hereinafter, acrylate includes acrylate itself and methacrylate,
and acrylate represents both), or 2-hydroxypropyl acrylate are
allowed to react with the product which is commonly prepared by
allowing polyester polyols to react with isocyanate monomers or
prepolymers. For example, those described in Japanese Patent O.P.I.
Publication No. 59-151110 can be used.
For example, preferably employed is a mixture comprising 100 parts
of Unidick 17-806 (manufactured by Dainippon Ink and Chemicals
Inc.) and one part of Coronate L (manufactured by Nippon Urethane
Industry Co., Ltd.).
The UW ray curable polyester acrylate resins include those prepared
easily by reacting a polyester polyol with 2-hydroxyethylacrylate
or 2-hydroxypropylacrylate, disclosed for example, in Japanese
Patent O.P.I. Publication No. 59-151112.
Examples of the UV ray curable epoxy acrylate resin include those
prepared by reacting an epoxy acrylate oligomer in the presence of
a reactive diluting agent and a photoinitiator, disclosed for
example, in Japanese Patent O.P.I. Publication No. 1-105738.
Examples of the UV ray curable polyol acrylate resin include
trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate,
pentaerythritol triacrylate, pentaerythritol tetraacrylate,
dipentaerythritol hexaacrylate or alkyl-modified dipentaerythritol
pentaacrylate.
The photoinitiators for the UV ray curable resins include benzoine
or its derivative, or acetophenones, benzophenones, hydroxy
benzophenones, Michler's ketone, .alpha.-amyloxime esters,
thioxanthones or their derivatives. an oxime ketone derivative, a
benzophenone derivative or a thioxanthone derivative. These
photoinitiators may be used together with a photo-sensitizer. The
above photoinitiators also work as a photo-sensitizer. Sensitizers
such as n-butylamine, triethylamine and tri-n-butylphosphine can be
used in photo-reaction of epoxyacrylates. The content of the
photoinitiators or sensitizers in the UV ray curable resin layer is
0.1 to 15 parts by weight, and preferably 1 to 10 parts by weight,
based on the 100 parts by weight of the UV ray curable resin
layer.
The polymerizable monomers having one unsaturated double bond in
the molecule include methyl acrylate, ethyl acrylate, butyl
acrylate, benzyl acrylate, cyclohexyl acrylate, vinyl acetate, and
styrene. The polymerizable monomers having two or more unsaturated
double bonds in the molecule include ethylene glycol diacrylate,
propylene glycol diacrylate, divinylbenzene, 1,4-cyclohexane
diacrylate, 1,4-cyclohexyldimethyl diacrylate, trimethylol propane
triacrylate, and pentaerythritol tetraacrylate.
The UV curable resins available on the market utilized in the
present invention include Adekaoptomer KR, BY Series such as
KR-400, KR-410, KR-550, KR-566, KR-567 and BY-320B (manufactured by
Asahi Denka Co., Ltd.); Koeihard A-101-KK, A-101-WS, C-302,
C-401-N, C-501, M-101, M-102, T-102, D-102, NS-101, FT-102Q8,
MAG-1-P20, AG-106 and M-101-C (manufactured by Koei Kagaku Co.,
Ltd.); Seikabeam PHC2210(S), PHC X-9(K-3), PHC2213, DP-10, DP-20,
DP=30, P1000, P1100, P1200, P1300, P1400, P1500, P1600, SCR900
(manufactured by Dainichiseika Kogyo Co., Ltd.); KRM7033, KRM7039,
KRM7131, UVECRYL29201 and UVECRYL29202 (manufactured by Daicel U.
C. B. Co., Ltd.); RC-5015, RC-5016, RC-5020, RC-5031, RC-5100,
RC-5102, RC-5120, RC-5122, RC-5152, RC-5171, RC-5180 and RC-5181
(manufactured by Dainippon Ink & Chemicals, Inc.); Olex No. 340
Clear (manufactured by Chyugoku Toryo Co., Ltd.); Sunrad H-601,
RC-750, RC-700, RC-600, RC-500, RC-611 and RC-612 (manufactured by
Sanyo Kaseikogyo Co., Ltd.); SP-1509 and SP-1507 (manufactured by
Syowa Kobunshi Co., Ltd.); RCC-15C (manufactured by Grace Japan
Co., Ltd.) and Aronix M-6100, M-8030 and M-8060 (manufactured by
Toagosei Co., Ltd.).
Concrete examples include trimethylol propane triacrylate,
ditrimethylol propane tetracrylate, pentaerythritol triacrylate,
pentaerythritol tetracrylate, dipentaerythritol hexaacrylate and
alkyl modified dipentaerythritol pentaacrylate.
These actinic ray curable resin layers can be applied by any method
well known in the art, for example: a gravure coater, a dip coater,
a reverse coater, a die coater and ink jet printing.
Light sources to cure layers of UV curable-resin by photo-curing
reaction are not specifically limited, and any light source may be
used as far as UV ray is generated. For example, a low-pressure
mercury lamp, a medium-pressure mercury lamp, a high-pressure
mercury lamp, an ultrahigh-pressure mercury lamp, a carbon arc
lamp, a metal halide lamp and a xenon lamp may be utilized. An air
cooling or a water cooling light source is preferably used. The
preferable irradiation quantity of light may be changed depending
on the type of lamp, however, it is preferably from 5 to 150
mj/cm.sup.2, and more preferably from 20 to 100 mJ/cm.sup.2.
The oxygen content at the irradiation area is preferably decreased
to 0.01-2% by purging with nitrogen.
Irradiation of an actinic ray is preferably carried out under
tension in the longitudinal direction of the film and more
preferably under tension in both the lateral and the longitudinal
directions. The preferable tension is from 30 to 300 N/m. The
method to provide tension is not specifically limited and following
methods are preferably used: (i) a method of providing tension
while the film is being transported over back rolls, and (ii) a
method using a tenter to give tension in the lateral direction or
in biaxial directions. A cellulose ester film exhibiting a superior
flatness can be obtained using these methods.
An organic solvent used for a coating solution of a UV
curable-resin can be selected from, for example, the hydrocarbon
series (toluene and xylene), the alcohol series (methanol, ethanol,
isopropanol, butanol and cyclohexanol), the ketone series (acetone,
methyl ethyl ketone and isobutyl ketone), the ester series (methyl
acetate, ethyl acetate and methyl lactate), the glycol ether series
and other organic solvents. These organic solvents may be also used
in combination. The above mentioned organic solvents preferably
contain propylene glycol monoalkyl ether (the alkyl having 1 to 4
carbon atoms) or propylene glycol monoalkyl ether acetate (the
alkyl having 1 to 4 carbon atoms) in an amount of 5% by weight or
more, and more preferably from 5 to 80% by weight.
In a coating solution of a UV ray-curable resin, a silicon compound
such as a polyether modified silicone oil, is preferably added. The
number average molecular weight of the polyether modified silicone
oil is preferably from 1,000 to 100,000 and more preferably from
2,000 to 50,000. Addition of the polyether modified silicone oil
with a number average molecular weight of less than 1,000 may lower
the drying rate of the coating solution, while that of more than
100,000 may be difficult to bleed out at the surface of the coated
film.
Silicon compounds available on the market include, for example:
DKQ8-779 (a trade name of Dow Corning Corp.), SF3771, SF8410,
SF8411, SF8419, SF8421, SF8428, SH200, SH510, SH1107, SH3771,
BX16-034, SH3746, SH3749, SH8400, SH3771M, SH3772M, SH3773M,
SH3775M, BY-16-837, BY-16-839, BY-16-869, BY-16-870, BY-16-004,
BY-16-891, BY-16-872, BY-16-874, BY22-008M, BY22-012M, FS-1265 (all
being trade names of Dow Corning Toray Silicone Co., Ltd.), KF-101,
KF-100T, KF351, KF352, KF353, KF354, KF355, KF615, KF618, KF954,
KF6004, siliconeX-22-945, X22-160AS (all being trade names of
Shin-Etsu Chemical Co., Ltd.), XF3940, XF3949 (both being trade
names of Toshiba Silicones Co., Ltd.), DISPARLONLS-009 (a trade
name of Kusumoto Chemicals Ltd.), GLANOL410 (a trade name of
Kyoeisha Chemicals Co., Ltd.), TSF4440, TSF4441, TSF4445, TSF4446,
TSF4452, TSF4460 (all being trade names of GE Toshiba Silicones
Co., Ltd.), BYK-306, BYK-330, BYK-307, BYK-341, BYK-361 (all being
trade names of BYK-Chemie Japan KK), L Series (L-7001, L-7006,
L-7604 and L-9000), Y Series and FZ Series (FZ-2203, FZ-2206 and
FZ-2207) (all from Nippon Unicar Co., Ltd.).
These compositions may improve the coating ability of a coating
solution onto a substrate or an under coat layer. These compounds
used in the top layer of film may contribute to improvement of
scratch resistance of the film as well as water-resistance,
oil-resistance and anti-stain properties of the film. The content
of the silicon compound is preferably from 0.01 to 3% by weight
based on the solid components in the coating solution.
The aforementioned coating methods are also used as coating method
of a UV ray-curable resin layer coating solution. The wet thickness
of the coated UV-curable resin layer is preferably from 0.1 to 30
.mu.m and more preferably from 0.5 to 15 .mu.m. The dry thickness
of the coated UV-curable resin layer is preferably from 0.1 to 20
.mu.m and more preferably from 1 to 10 .mu.m.
The UV ray-curable resin layer is preferably irradiated with UV
rays during or after drying. The duration of UV ray irradiation is
preferably from 0.1 seconds to 5 minutes in order to secure the
exposure amount from 5 to 100 mJ/cm.sup.2 as mentioned above. In
view of working efficiency and hardening efficiency of the
UV-curable resin layer, the duration is more preferably from 0.1 to
10 seconds.
Intensity of the actinic ray is preferably from 50 to 150
mW/cm.sup.2 on the irradiated surface.
The UV-cured resin layer thus obtained may preferably contain
inorganic or organic particles in order to attain the following
characteristics: (i) preventing blocking, (ii) improving scratch
resistance, (iii) providing an antiglare property and (iv)
optimizing the reflective index.
The hard coat layer of the present invention preferably contains
inorganic particles, examples of which include, for example:
silicon oxide, titanium oxide, aluminum oxide, zirconium oxide,
magnesium oxide, calcium carbonate, talc, clay, calcined kaolin,
calcined calcium silicate, hydrated calcium silicate, aluminum
silicate, magnesium silicate and calcium phosphate. Among these,
silicon oxide, titanium oxide, aluminum oxide, zirconium oxide,
magnesium oxide are specifically preferable.
Organic particles include, for example: particles of
polymethacrylic acid methyl acrylate resin, acryl styrene based
resin, polymethyl methacrylate resin, silicon based resin,
polystyrene based resin, polycarbonate resin, benzoguanamine based
resin, melamine based resin, polyolefin based resin, polyester
based resin, polyamide based resin, polyimide based resin and
polyfluorinated ethylene based resin. Specifically preferable
organic particles include, for example: particles of cross-linked
polystylene (such as SX-130H, SX-200H and SX-350H manufactured by
Soken Chemical & Engineering Co., Ltd.) and polymethyl
methacrylate (such as MX150 and MX300 manufactured by Soken
Chemical & Engineering Co., Ltd.).
The average particle diameter of the particles is preferably from
0.005 to 5 .mu.m and specifically preferably from 0.01 to 1 .mu.m.
The particle content of the hard coat layer is preferably from 0.1
to 30 weight parts per 100 weight parts of the UV-curable resin
composition.
It is preferred that the UV curable resin layer is a clear hard
coat layer having a center-line average roughness (Ra prescribed by
JIS B 0601) of 1 to 50 nm or an anti-glare layer Having an Ra value
of from 0.1 to 1 .mu.m. The center-line average roughness (Ra) is
preferably measured by means of a surface roughness meter using
interference of light, for example, RST/PLUS manufactured by WYKO
Co., Ltd.
The hard coat layer of the present invention may preferably contain
an antistatic agent. For example, preferable are an electrically
conductive material containing as a main ingredient at least one of
the element selected from the group of Sn, Ti, In, Al, Zn, Si, Mg,
Ba, Mo, W and V, and having a volume resistivity of not more than
10.sup.7 ohmcm.
Examples of the antistatic agent also include: oxides and complex
oxides of the above described elements.
Examples of a metal oxide include: ZnO, TiO.sub.2, SnO.sub.2,
Al.sub.2O.sub.3, In.sub.2O.sub.3, SiO.sub.2, MgO, BaO, MoO.sub.2,
V.sub.2O.sub.5 and complex metal oxides thereof. Of these,
specifically preferable are, for example, ZnO, In.sub.2O.sub.3,
TiO.sub.2, and SnO.sub.2. As examples of indroduction of foreign
element, effective are, (i) introduction of, for example, Al or In
in ZnO; (ii) introduction of, for example, Nb or Ta in TiO.sub.2;
and (iii) introduction of, for example, Sb, Nb or a halogen atom in
SnO.sub.2. The amount of the foreign element is preferably 0.01-25
mol % and specifically preferably 0.1-15 mol %. The volume
resistivity of these conductive metal oxide powder is preferably
107 ohmcm or less and specifically preferably 105 ohmcm or
less.
(Antireflection Layer)
The polarizing plate protective film of the present invention
preferably has an antireflection layer as a functional layer on the
above mentioned hard coat layer, and specifically preferable is to
have a low refractive index layer containing hollow particles.
(Low Refractive Index Layer)
The low refractive index layer of the present invention preferably
contains hollow particles, and, in addition, preferably contains
silicon alkoxide, a silane coupling agent and a hardening
agent.
<Hollow Particles>
In the low refractive index layer, hollow particles described below
are preferably incorporated.
The hollow particles can be classified into (1) the composite
particles made of porous particle and the coated layer arranged on
this porous particle surface; and (2) the hollow particles that
have a hollow interior filled with solvent, gas or porous
substances. The low-refractive index layer coating solution may
contain (1) composite particles and/or (2) hollow particles.
The hollow particles have a hollow interior which is surrounded
with particle walls. The cavity is filled with the solvent used at
the time of preparation, gas or porous substances. The average
particle diameter of such inorganic particles is preferably 5-300
nm, more preferably 10-200 nm. The inorganic particles to be used
is properly selected according to the thickness of the transparent
coating layer to be formed. The diameter is preferably 2/3- 1/10
that of the transparent coating layer such as low-refractive index
layer to be formed. For formation of the low-refractive index
layer, these hollow particles are preferably used as they are
dispersed in a proper medium. The preferred dispersion medium
includes water, alcohol (e.g. methanol, ethanol, isopropyl alcohol)
and ketone (e.g. methyl ethyl ketone and methyl isobutyl ketone)
and ketone alcohol (e.g. diacetone alcohol).
The thickness of the coated layer of the composite particle or
hollow particle wall is preferably 1-20 nm and more preferably,
2-15 nm. In the case of the composite particle, if the thickness of
the coated layer is less than 1 nm, the particles may not
completely be covered, resulting in reducing the effect of the
low-refractive index layer. If the thickness of the coated layer
exceeds 20 nm, the porosity (porous volume) of the composite
particle may be reduced, resulting in reducing the effect of the
low-refractive index layer. In the case of hollow particles, if the
thickness of the particle wall is less than 1 nm, the shape of the
particle may not be maintained. If the thickness exceeds 20 nm, a
sufficient effect of low-refractive index may not be obtained.
The coated layer of the composite particle or hollow particle wall
is preferably made of silica as a main component. A component other
than silica may be contained, of which specific examples include:
Al.sub.2O.sub.3, B.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, SnO.sub.2,
CeO.sub.2, P.sub.2O.sub.3, Sb.sub.2O.sub.3, MoO.sub.3, ZnO and
WO.sub.3. The porous particles constituting composite particle
include: (i) those composed of silica; (ii) those composed of
silica and inorganic compound other than silica; and (iii) those
composed of CaF.sub.2, NaF, NaAlF.sub.6, or MgF.sub.2. Of these,
the porous particles made of composite oxide of silica and
inorganic compound other than silica are preferably used. The
inorganic compound other than silica can be exemplified by the
compound made of one or two of: Al.sub.2O.sub.3, B.sub.2O.sub.3,
TiO.sub.2, ZrO.sub.2, SnO.sub.2, CeO.sub.2, P.sub.2O.sub.3,
Sb.sub.2O.sub.3, MoO.sub.3, ZnO and WO.sub.3. In such porous
particles, silica is expressed by SiO.sub.2 and the inorganic
compound other than silica is represented by the equivalent oxide
(MOx). In this case, the mole ratio MOx/SiO.sub.2 is preferably
within the range of 0.0001-1.0, more preferably 0.001-0.3.
Particles cannot be easily obtained if the mole ratio MOx/SiO.sub.2
of the porous particle is less than 0.0001. Even if it can be
obtained, the pore volume will be small, and the particle of small
refractive index cannot be obtained. If the mole ratio
MOx/SiO.sub.2 of the porous particle exceeds 1.0, the content of
silica is reduced, hence the pore volume will be increased. This
may make it all the more difficult to get the particles giving a
low refractive index.
The pore volume of such porous particles is preferably 0.1-1.5
ml/g, more preferably 0.2-1.5 ml/g. If the pore volume is less than
0.1 ml/g, the particles of sufficiently reduced refractive index
cannot be ensured. If it exceeds 1.5 ml/g, the strength of the
particles will be reduced, hence the strength of the produced film
may be reduced.
The pore volume of such porous particle can be determined by the
method of mercury penetration. The contents inside the hollow
particle can be exemplified by the solvent, gas and porous
substance used at the time of preparing the particles. The solvent
may contain the unreacted substances of the particle precursor and
the catalysts used at the time of preparing the hollow particle.
The porous substances includes the compounds listed with reference
to the aforementioned porous particle. These contents may be made
of a single compound or a mixture of a plurality of compounds.
To produce such inorganic particles, the composite oxide colloid
particle preparation methods disclosed in the paragraph numbers
[0010] through [0033] of JP-A No. 7-133105 are preferably employed.
To put it more specifically, when the composite particle is made of
silica and inorganic compound other than silica, the hollow
particles are manufactured according to the first through third
Steps given below:
1st Step: Preparation of Porous Particle Precursor
In the first Step, aqueous alkaline solutions of silica material
and inorganic compound material other than silica are prepared
separately in advance or, the aqueous solution of a mixture of
silica material and inorganic compound material other than silica
is prepared. In response to the percentage of the composite of the
intended composite oxide, this aqueous solution is added, with
stirring, gradually into the alkaline solution having a pH greater
than 10, whereby the porous particle precursor is prepared.
The silicate of alkali metal, ammonium or organic base is used as a
silica material. Sodium silicate (water glass) or potassium
silicate is utilized as the silicate of alkali metal. The organic
base can be exemplified by quaternary ammonium salts such as
tetraethyl ammonium salts, and amines such as monoethanol amine,
diethanol amine and triethanol amine. The silicates of the ammonium
or silicates of the organic salts also includes alkaline solution
obtained by adding ammonia, quaternary ammonium hydroxide and amine
compound to the silica solution.
As the inorganic compound material other than silica, alkali
soluble conductive materials described above are used.
The pH value of the aqueous mixture solution undergoes changes with
addition of these aqueous solution. However, it is not necessary to
control this pH value within the predetermined range. In the final
phase, the aqueous solution has the pH value determined by the type
of the inorganic oxide and its bending ratio. There is no
restriction to the speed of adding the aqueous solution in this
case. Further, when the composite oxide particle is manufactured,
the aqueous dispersion of the seed particle can be used as the
starting material. There is no particular restriction on this seed
particle. The particles made of inorganic oxide such as SiO.sub.2,
Al.sub.2O.sub.3, TiO.sub.2 or ZrO.sub.2 or the composite oxide
thereof are utilized. Normally, the sol thereof can be used.
Further, the porous particle precursor aqueous dispersion obtained
according to the aforementioned production method can be used as
seed particle aqueous dispersion. When the seed particle aqueous
dispersion is used, the pH value of seed particle aqueous
dispersion is adjusted to 10 or more. After that, the aqueous
solution of the aforementioned compound is added to this seed
particle aqueous dispersion, being stirred in aqueous alkaline
solution. In this case, the pH value of the aqueous dispersion need
not necessarily be controlled. Use of the seed particles are used
in this manner, ensures easy control of the diameter of the porous
particle to be prepared, and provides uniform particle sizes.
The aforementioned silica material and inorganic compound material
exhibit a high degree of solubility on the alkali side. However, if
they are mixed in the pH region where the solubility is high, the
solubility of the oxo acid such as silica ion and aluminic acid ion
will be reduced. Their composites will be deposited to grow into
particles. Alternatively, they will be deposited on the seed
particle to cause particle growth. This being the case, pH control
is not always necessary at the time of deposition and growth of the
particles, as in the conventional method.
The ratio of composition of silica and inorganic compound other
than silica in the first Step is determined as follows: The
inorganic compound with respect to silica is converted into the
equivalent oxide (MO.sub.x), and the mole ratio of the
MO.sub.x/SiO.sub.2 is kept preferably within the range of 0.05-2.0,
more preferably 0.2-2.0. The small the ratio of silica within this
range, the greater the pore volume of the porous particle. However,
even if the mole ratio is over 2.0, the pore volume of the porous
particle hardly increases. If the mole ratio is less than 0.05, the
pore volume reduces. When the hollow particle is prepared, the mole
ratio of the MOx/SiO.sub.2 is preferably 0.25-2.0.
2nd Step: Removal of the Inorganic Compound Other than Silica from
the Porous Particle
In the second Step, at least part of the inorganic compound other
than silica (elements other than silicon and oxygen) is removed on
a selective basis from the porous particle precursor having been
obtained in the aforementioned first Step. To put it more
specifically, the inorganic compound in the porous particle
precursor is dissolved and removed by mineral acid and organic
acid. Alternatively, it is brought in contact with a positive ion
exchange resin and is removed by ion exchange.
The porous particle precursors obtained in the first Step are the
particle of a network structure composed of a silicon and inorganic
compound constituent element bonded together through oxygen. As
described above, the porous particles characterized by one layer of
porous structure and greater pore volume are provided by removing
the inorganic compound (elements other than silicon and oxygen)
from the porous particle precursor. Hollow particles can be
prepared by increasing the amount of the inorganic compound
(elements other than silicon and oxygen) removed from the porous
particle precursor.
Before removing the inorganic compound (elements other than silicon
and oxygen) from the porous particle precursor, silica solution or
hydrolytic organic silicon compound, obtained by dealkalization of
the alkali metal salt of silica, is preferably added to the porous
particle precursor aqueous dispersion obtained in the first Step,
whereby a silica protective film is formed. It is sufficient only
if silica protective film has a thickness of 0.5-15 nm. Even if a
silica protective film is formed, the protective film in this Step
is porous and is less thick. Such being the case, the
aforementioned inorganic compound other than silica can be removed
from the porous particle precursor.
By forming such a silica protective film, the aforementioned
inorganic compound other than silica can be removed from the porous
particle precursor, with the shape of the particle kept unchanged.
When forming the silica coated layer to be described later, porous
particle pores are not blocked by the coated layer. This makes it
possible to form the silica coated layer (to be described later)
without the pore volume being reduced. When a small amount of
inorganic compound is removed, the particles are not damaged.
Accordingly, formation of a protective film is not imperative.
When hollow particles are prepared, this silica protective film is
preferably formed. If the inorganic compound is removed in
preparing hollow particles, a hollow particle precursor is
obtained, wherein this hollow particle precursor is made of silica
protective film, solvent inside this silica protective film and
undissolved porous solid. If the coated layer to be described later
is formed on this hollow particle precursor, the coated layer
having been formed becomes a particle wall and hollow particles are
formed.
The amount of the silica source added to form the aforementioned
silica protective film is preferably as small as possible without
damaging the particle shape. If the amount of silica source is
excessive, the silica protective film will be too thick. This may
make it difficult to remove the inorganic compound other than
silica from the porous particle precursor. The alkoxy silane
expressed by the formula R.sub.nSi (OR').sub.4-n[R,R': hydrocarbon
group such as alkyl group, aryl group, vinyl group and acryl group;
n=0, 1, 2 or 3] can be used as a hydrolytic organic silicon
compound used to form the silica protective film. Specifically,
tetraalkoxy silane such as tetramethoxysilane, tetraethoxysilane
and tetraisoprophoxysilane is preferably utilized.
The following procedure is used for addition: The solution prepared
by adding a small quantity of alkali or acid as the catalyst to the
mixture solution of the alkoxy silane, demineralized water and
alcohol is added to the aqueous dispersion of the aforementioned
porous particle. The silica polymer generated by hydrolysis of the
alkoxy silane is deposited on the surface of the inorganic oxide
particle. In this case, the alkoxy silane, alcohol, catalyst can be
added simultaneously in the aqueous dispersion. Ammonia, hydroxide
of alkali metal and amines can be used as the alkali catalyst.
Varieties of inorganic and organic acids can be used as acid
catalyst.
When the dispersion medium of the porous particle precursor is
water alone or contains a high proportion of water with respect to
the organic solvent, silica solution can be used to form a silica
protective film. When the silica solution is used, a predetermined
amount of silica solution is added to the aqueous dispersion. At
the same time, alkali is added so that silica solution is deposited
on the porous particle surface. A silica protective film can be
produced by a combined use of the silica solution and the
aforementioned alkoxy silane.
3rd Step: Formation of Silica Coated Layer
In the third step, the hydrolytic organic silicon compound or
silica solution is added to the porous particle aqueous dispersion
(hollow particle precursor aqueous dispersion in the case of the
hollow particle) prepared in the second Step. This procedure
ensures that the particle surface is covered with the polymer such
as the hydrolytic organic silicon compound or silica solution,
whereby a silica coated layer is formed.
The alkoxy silane expressed by the aforementioned formula
R.sub.nSi(OR').sub.4-n[R,R': hydrocarbon group such as alkyl group,
aryl group, vinyl group and acryl group; n=0, 1, 2 or 3] can be
used as the hydrolytic organic silicon compound used for forming
the silica coated layer. Especially, the tetraalkoxy silane such as
tetramethoxysilane, tetraethoxysilane and tetraisoprophoxysilane is
preferably used.
The following procedure is taken for addition: The solution
prepared by adding a small quantity of alkali or acid as the
catalyst to the mixture solution of the alkoxy silane,
demineralized water and alcohol is added to the aqueous dispersion
of the aforementioned porous particle (hollow particle precursor in
this case of the hollow particle). The silica polymer generated by
hydrolysis of the alkoxy silane is deposited on the surface of the
porous particle (hollow particle precursor in this case of the
hollow particle). In this case, the alkoxy silane, alcohol,
catalyst can be added simultaneously in the aqueous dispersion.
Ammonia, hydroxide of alkali metal and amines can be used as the
alkali catalyst. Varieties of inorganic and organic acids can be
used as acid catalyst.
When the dispersion medium of the porous particle (hollow particle
precursor in this case of the hollow particle) is water alone or
the solution of mixture with the organic solvent wherein the
proportion of water is high with respect to the organic solvent,
then silica solution can be used to form a silica protective film.
The silica solution refers to the aqueous solution of the low
polymer of silica obtained by dealkalization of aqueous solution of
alkali metal silicate such as water glass through ion exchange
treatment.
The silica solution is added to the porous particle (hollow
particle precursor in this case of the hollow particle) aqueous
dispersion. At the same time, alkali is added so that the silica
low-polymer is deposited on the surfaced of the porous particle
(hollow particle precursor in this case of the hollow particle).
The silica solution can be used in combination with the
aforementioned alkoxy silane so that a coated layer is formed. The
amount of organic silicon compound or silica solution added to form
the coated layer should be such that the surface of the colloid
particle is sufficiently covered. The organic silicon compound or
silica solution is added in the dispersion of the porous particle
(hollow particle precursor in this case of the hollow particle), in
such an amount that the silica coated layer obtained in the final
phase has a thickness of 1-20 nm. When the aforementioned silica
protective film has been formed, the organic silicon compound or
silica solution is added in such an amount that the total of the
thicknesses of the silica protective film and silica coated layer
is within the range of 1-20 nm.
Then the aqueous dispersion of the particles of which the coated
layer is formed is subjected to heating. In the case of porous
particles, the silica coated layer covering the porous particle
surface is made compact by heating, thereby producing the
dispersion of composite particles wherein porous particles are
covered with the silica coated layer. In the case of hollow
particle precursor, the coated layer having been formed is made
compact and becomes a hollow particle wall, thereby producing the
dispersion of hollow particles having a cavity filled with solvent,
gas or porous solid.
There is no particular restriction to the heating temperature in
this case, if the microscopic pore of the silica coated layer can
be blocked. The heating temperature is preferably within the range
of 80-300.degree. C. If the heating temperature is less than
80.degree. C., the microscopic pore of the silica coated layer may
be completely blocked and may not be made compact. Alternatively, a
longer time will be required in some cases. If the heating
temperature is over 300.degree. C., compact particles may be
produced and the advantages of low-refractive index cannot be
ensured in some cases.
The refractive index of the inorganic particles obtained in this
manner is as low as less than 1.44. In such inorganic particles,
the porosity inside the porous particle or the interior is void.
This is estimated to cause low refractive index.
It is preferable that other than hollow particles, the low
refractive index layer incorporates hydrolyzed products of
alkoxysilicon compounds and condensation products which are formed
via the following condensation reaction. It is particularly
preferable to incorporate a SiO.sub.2 sol prepared employing the
alkoxysilicon compounds represented by following Formula (4) and/or
(5) or hydrolyzed products thereof. R1-Si(OR.sub.2).sub.3 Formula
(4) Si(OR.sub.2).sub.4 Formula (5) wherein R1 represents a methyl
group, an ethyl group, a vinyl group, or an organic group
incorporating an acryloyl group, a methacryloyl group, an amino
group, or an epoxy group, and R2 represents an methyl group or an
ethyl group.
Hydrolysis of silicon alkoxide and silane coupling agents is
performed by dissolving the above in suitable solvents. Examples of
used solvents include ketones such as methyl ethyl ketone, alcohols
such as methanol, ethanol, isopropyl alcohol, or butanol, esters
such as ethyl acetate, or mixtures thereof.
Water in a slightly larger amount for hydrolysis is added to a
solution prepared by dissolving the above silicon alkoxide or
silane coupling agents in solvents, and the resulting mixture is
stirred at 15-35.degree. C. but preferably 20-30.degree. C. for
1-48 hours but preferably 3-36 hours.
It is preferable to employ catalysts during the above hydrolysis.
Preferably employed as such catalysts are acids such as
hydrochloric acid, nitric acid, or sulfuric acid. These acids are
employed in the form of an aqueous solution at a concentration of
0.001-20.0 N, but preferably 0.005-5.0 N. It is possible to employ
water in the above aqueous catalyst solution as water for
hydrolysis.
Alkoxysilicon compounds undergo hydrolysis over the specified
period of time, and the hydrolyzed alkoxysilicon solution is
diluted with solvents, followed by the addition of other necessary
additives, whereby a low refractive index layer liquid coating
composition is prepared. It is possible to form a low refractive
index layer on a substrate by applying the above liquid coating
composition onto a substrate such as a film followed by drying.
<Alkoxysilicon Compounds>
In the present invention, preferred as alkoxysilicon compounds
(hereinafter also referred to as alkoxysilanes) employed to prepare
the low refractive index layer liquid coating composition are those
represented by following Formula (6). R4-nSi(OR')n Formula (3)
wherein R' represents an alkyl group; R represents a hydrogen atom
or a univalent substituent; and n represents 3 or 4.
The alkyl groups represented by R' include groups such as a methyl
group, an ethyl group, a propyl group, or a butyl group, which may
have a substituent. The substituents are not particularly limited
as long as characteristics as an alkoxysilane are maintained.
Examples of such substituents include a halogen atom such as
fluorine and an alkoxy group, but unsubstituted alkyl groups are
more preferred. Particularly preferred are a methyl group and an
ethyl group.
The univalent substituents represented by R are not particularly
limited, and examples include an alkyl group, a cycloalkyl group,
an alkenyl group, an aryl group, an aromatic heterocyclyl group,
and a silyl group. Of these, preferred are an alkyl group, a
cycloalkyl group, and an alkenyl group. These may be further
substituted. Cited as substituents of R are a halogen atom such as
a fluorine atom or a chlorine atom, an amino group, an epoxy group,
a mercapto group, a hydroxyl group, and an acetoxy group.
Specific preferable examples of the alkoxysilane represented by the
above formula include tetramethoxysilane, tetraethoxysilane (TEOS),
tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane,
tetra-t-butoxysilane, tetrakis(methoxyethoxy)silane,
tetrakis(methoxypropoxy)silane, methyltrimethoxysilane,
methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,
n-propyltrimethoxysilane, n-propyltriethoxysilane,
n-butyltrimethoxysilane, i-butyltrimethoxysilane,
n-hexyltrimethoxysilane, 3-glycycloxyproyltrimethoxysilane,
3-aminopropyltriethoxysilane,
2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,
acetoxytriethoxysilane,
(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane,
(3,3,3-trifluoropropyl)trimethoxysilane,
(3,3,3-trifluoropropyl)trimethoxysilane,
pentafluorophenylpropyltrimethoxysilane, further
vinyltrimethoxysilane, vinyltriethoxysilane,
phenyltrimethoxysilane, vinyltrimethoxysilane, and
vinyltriethoxysilane.
Further, included may be silicon compounds in the form of oligomers
such as SILICATE 40, SILICATE 45, SILICATE 48, and M SILICATE 51,
produced by Tamagawa Chemical Co., which are partial condensation
products of the above compounds.
Since the above alkoxysilanes incorporate silicon alkoxide group
capable of undergoing hydrolysis polycondensation, the network
structure of polymer compounds is formed in such a manner that
these alkoxysilanes undergo hydrolysis, condensation and
crosslinking. The resulting composition is employed as a low
refractive index layer liquid coating composition which is applied
onto a substrate and dried, whereby a layer uniformly incorporating
silicon oxide is formed on the substrate.
It is possible to perform a hydrolysis reaction employing the
method known in the art. Hydrophilic alkoxysilanes are dissolved in
a mixture of water of the specified amount and hydrophilic organic
solvents such as methanol, ethanol, or acetonitrile so that
alkoxysilanes are compatible with solvents. After the addition of
hydrolysis catalysts, alkoxysilanes undergo hydrolysis and
condensation. By performing the hydrolysis and condensation
reaction commonly at 10-100.degree. C., silicate oligomers in a
liquid state, having at least two hydroxyl groups, are formed,
whereby a hydrolyzed liquid composition is prepared. It is possible
to appropriately control the degree of hydrolysis varying the
amount of employed water.
In the present invention, preferred as solvents added to
alkoxysilanes together with water are methanol and ethanol since
they are less expensive and form a layer exhibiting excellent
characteristics and desired hardness. It is possible to employ
isopropanol, n-butanol, isobutanol, and octanol, while the hardness
of the resulting layer tends to decrease. The amount of solvents is
commonly 50-400 parts by weight with respect to 100 parts by weight
of tetraalkoxysilanes prior to hydrolysis, but is preferably
100-250 parts by weight.
The hydrolyzed liquid composition is prepared as described above.
The above composition is diluted with solvents, and if desired,
added with additives. Subsequently, components required to form a
low refractive index layer liquid coating composition are mixed,
whereby a low refractive index layer liquid coating composition is
prepared.
Cited as hydrolysis catalysts may be acids, alkalis, organic
metals, and metal alkoxides. In the present invention, preferred
are inorganic acids such as sulfuric acid, hydrochloric acid,
nitric acid, hypochlorous acid, or boric acid, or organic acids. Of
these, particularly preferred are nitric acid, carboxylic acids
such as acetic acid, polyacrylic acid, benzenesulfonic acid,
paratoluenesulfonic acid, and methylsulfonic acid. Of these, most
preferably employed are nitric acid, acetic acid, citric acid, and
tartaric acid. Other than above citric acid and tartaric acid, also
preferably employed are levulinic acid, formic acid, propionic
acid, malic acid, succinic acid, methylsuccinic acid, fumaric acid,
oxalacetic acid, pyruvic acid, 2-oxoglutaric acid, glycolic acid,
D-glyceric acid, D-gluconic acid, malonic acid, maleic acid, oxalic
acid, isocitric acid, and lactic acid.
Among the above catalysts, preferred are those which do not remain
in the layer via evaporation during drying and also exhibit a low
boiling point. Accordingly, acetic acid and nitric acid are most
preferred.
The added amount is commonly 0.001-10 parts by weight with respect
to 100 parts by weight of the employed alkoxysilicon compounds (for
example, tetraalkoxysilane), but is preferably 0.005-5 parts by
weight. Further, the added amount of water is to be at least the
amount capable of performing theoretically 100% hydrolysis of the
compound to be hydrolyzed. It is recommended to add water in an
equivalent amount of 100-300%, but preferably of 100-200%.
During the hydrolysis of the above alkoxysilanes, it is preferable
to blend the following inorganic particles.
After initiation of hydrolysis, a hydrolyzed liquid composition is
allowed to stand over the specified period of time. After the
hydrolysis reaches the specified degree, the above catalysts are
employed. The standing period refers to the sufficient period
during which the above hydrolyses and crosslinking due to
condensation are progressed to result in desired layer
characteristics. The specific period varies depending on the type
of acid catalysts, but when acetic acid is employed, the period is
at least 15 hours at room temperature, while when nitric acid is
employed, the period is preferably at least two hours. Ripening
temperature affects ripening temperature. Generally, at a higher
temperature, ripening is more promoted. However, since gelling
occurs at more than or equal to 100.degree. C., it is appropriate
to raise and maintain the temperature between 20-60.degree. C.
The silicate oligomer solution prepared by performing hydrolysis
and condensation as described above is added with the above hollow
particles and additives, and the resulting mixture is diluted as
required, whereby a low refractive index layer liquid coating
composition is prepared. Subsequently, the resulting coating
composition is applied onto the above film, whereby it is possible
to form a layer as a low refractive index layer composed of an
excellent silicon oxide layer.
Further, in the present invention, other than the above
alkoxysilanes, employed may be the compounds which are prepared by
modifying silane compounds (being monomers, oligomers, or polymers)
having a functional group such as an epoxy group, an amino group,
an isocyanate group, or a carboxyl group, and may be employed
individually or in combination.
(Fluorine Compounds)
It is preferable that the low refractive index layer employed in
the present invention incorporates hollow particles and fluorine
compounds, and also incorporates fluorine containing resins
(hereinafter also referred to as "pre-crosslinking fluorine
containing resins"), which undergo crosslinking via heat or
ionizing radiation. By incorporating the above fluorine containing
resins, it is possible to provide a desired stain resistant
antireflection film.
Preferably listed as such fluorine containing resins prior
crosslinking may be fluorine containing copolymers which are formed
employing fluorine containing vinyl monomers and monomers to
provide a crosslinking group. Specific examples of the above
fluorine containing vinyl monomer units include fluoroolefins (for
example, fluoroethylene, vinylidene fluoride, tetrafluoroethylene,
hexafluoroethylene, hexafluoropropylene, or
perfluoro-2,2-dimethyl-1,3-dioxonol), and alkylester derivatives in
which (meth)acrylic acid is partially or completely fluorinated
(for example, VISCOAT 6FM (produced by Osaka Yuki Kagaku Co.), or
M-2020 (produced by Daikin Co.), completely or partially
fluorinated vinyl ethers. Cited as monomers to provide a
crosslinking group are vinyl monomers which previously incorporate
a crosslinking functional group in the molecule such as glycidyl
methacrylate, vinyltrimethoxysilane,
.gamma.-methacryloyloxypropyltrimethoxysilane, vinyl glycidyl
ether, and in addition, vinyl monomers having a carboxyl group, a
hydroxyl group, an amino group, or a sulfone group (for example,
(meth)acrylic acid, methylol (meth)acrylate, hydroxyalkyl
(meth)acrylate, allyl acrylate, hydroxyalkyl vinyl ether, or
hydroxyalkyl allyl ether). JP-A Nos. 10-25388 and 10-147739
describe that it is possible to introduce, after copolymerization,
a crosslinking structure to the latter via the addition of
compounds having a group capable of reacting with a functional
group in the polymers and at least one reactive group. Examples of
such crosslinking groups include an acryloyl, methacryloyl,
isocyanate, epoxy, aziridine, oxazolidine, aldehyde, carbonyl,
hydrazine, carboxyl, methylol, or active methylene group. Cases, in
which fluorine containing polymers react with a crosslinking group
upon being heated, or undergo crosslinking upon being heated via
combinations such as an ethylenic unsaturated group and a thermally
radical generating agent, or an epoxy group and a thermally acid
generating agents, are designated as a thermal curing type. On the
other hand, cases in which crosslinking is performed via
combination of an ethylenic unsaturated group and a photolytically
radical generating agent or an epoxy group and a photolytically
acid generating agent upon being exposed to radiation (preferably
ultraviolet radiation or electron beams), is designated as an
ionizing radiation curing type.
In addition to the above monomers, employed as pre-crosslinking
fluorine containing resins may be fluorine containing copolymers
which are prepared simultaneously employing monomers other than the
fluorine containing vinyl monomers and monomers to provide a
crosslinking group. Simultaneously usable monomers are not
particularly limited and may include olefins (such as ethylene,
propylene, isoprene, vinyl chloride, or vinylidene chloride);
acrylic acid esters (such as methyl acrylate, ethyl acrylate, or
2-etylhexyl acrylate); methacrylic acid esters (such as methyl
methacrylate, ethyl methacrylate, butyl methacrylate, or ethylene
glycol dimethacrylate); styrene derivatives (such as styrene,
divinylbenzene, vinyltoluene, or .alpha.-methylstyrene); vinyl
ethers (such as methyl vinyl ether); vinyl esters (such as vinyl
acetate, vinyl propionate, or vinyl cinnamate); acrylamides (such
as N-tert-butyl acrylamide or N-cyclohexyl acrylamide);
methacrylamides; and acrylonitrile derivatives. Further, in order
to provide lubrication and stain resistance, it is preferable to
introduce a polyorganosiloxane skeleton and a perfluoropolyether
skeleton into the fluorine containing copolymers. Such skeletons
are formed via polymerization of polyorganosiloxane having a
terminal group such as an acryl group, a methacryl group, a vinyl
ether group, or a styryl group with the above monomers,
polymerization of the above monomers with polyorgsanosiloxane
having a radical generating group at the terminal or
perfluoropolyether, or reaction of polyorganosiloxane having a
functional group at the terminal or perfluoropolyether.
The used ratio of each of the above monomers employed to from the
fluorine containing copolymers prior to crosslinking is preferably
20-70 mol % with respect to the fluorine containing vinyl monomers,
but is more preferably 40-70 mol % and the used ratio of monomers
to provide a crosslinking group is preferably 1-20 mil %, but is
more preferably 5-20 mol %, while the ratio of simultaneously
employed other monomers is preferably 10-70 mol %, but is more
preferably 10-50 mol %.
It is possible to prepare fluorine containing copolymers via
polymerization in the presence of radical polymerization
initiators, employing methods such as solution polymerization, bulk
polymerization, emulsion polymerization, or suspension
polymerization.
Pre-crosslinking fluorine containing resins are commercially
available. Examples of commercially available pre-crosslinking
fluorine containing resins include SAITOP (produced by Asahi Glass
Co.), TEFLON (registered trade name) AF (produced by DuPont),
polyvinylidene fluoride, RUMIFRON (produced by Asahi Glass Co.),
and OPSTAR (produced by JSR).
The Dynamic friction coefficient and the contact angle to water of
the low refractive index layer composed of crosslinked fluorine
containing resins are preferably in the range of 0.03-0.15 and
90-120 degrees, respectively.
<Additives>
If desired, it is possible to incorporate additives such as silane
coupling agents or hardening agents in the low refractive index
liquid coating composition. The silane coupling agents are the
compounds represented by above Formula (2).
Specific examples include vinyltriethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, and
3-(2-aminoethylaminopropyl)trimethoxysilane.
Cited as hardening agents are organic acid metal salts such as
sodium acetate or lithium acetate, of which sodium acetate is
particularly preferred. The added amount to the siliconalkoxysilane
hydrolyzed solution is preferably in the range of about 0.1--about
1 part by weight with respect to 100 parts by weight of solids in
the hydrolyzed solution.
Further, it is preferable to add, to the low refractive index layer
employed in the present invention, various leveling agents, surface
active agents, and low surface tension substances such as silicone
oil.
Specific commercially available silicone oils include L-45, L-9300,
FZ-3704, FZ-3703, FZ-3720, FZ-3786, FZ-3501, FZ-3504, FZ-3508,
FZ-3805, FZ-3707, FZ-3710, FZ-3750, FZ-3760, FZ-3785, FZ-3785, and
Y-7400 of Nippon Unicar Co., Ltd., as well as KF96L, KF96, KF96H,
KF99, KF54, KF965, KF968, KF56, KF995, KF351, KF352, KF353, KF354,
KF355, KF615, KF618, KF945, KF6004, and FL100 of Shin-Etsu Chemical
Co., Ltd.
These components enhance coatability onto a substrate or a lower
layer. When incorporated in the uppermost layer of the multicoated
layers, water- and oil-repellency, and anti-staining are enhanced
and in addition, abrasion resistance of the surface is also
enhanced. Since the excessive addition of these components results
in repellency during coating, the added amount is preferably in the
range of 0.01-3% by weight with respect to the solids in the liquid
coating composition.
<Solvents>
Solvents employed in the liquid coating composition during coating
the low refractive index layer include alcohols such as methanol,
ethanol, 1-propanol, 2-propanol, or butanol; ketones such as
acetone, methyl ethyl ketone, or cyclohexanone; aromatic
hydrocarbons such as benzene, toluene, or xylene; glycols such as
ethylene glycol, propylene glycol, or hexylene glycol; glycol
ethers such as ethyl cellosolve, butyl cellosolve, ethyl CARBITOL,
butyl CARBITOL, diethyl cellosolve, diethyl CARBITOL, or propylene
glycol monomethyl ether; N-methylpyrrolidone, dimethylformamide,
methyl lactate, ethyl lactate, methyl acetate, and water. These may
be employed individually or in combinations of at least two
types.
<Coating Methods>
The low refractive index layer is coated employing the methods
known in the art, such as dipping, spin coating, knife coating, bar
coating, air doctor coating, curtain coating, spray costing, or die
coating, as well as ink-jet methods known in the art. Coating
methods which enable continuous coating and thin layer coating are
preferably employed. The coated amount is commonly 0.1-30 .mu.m in
term of wet thickness, but is preferably 0.5-15 .mu.m. The coating
rate is preferably 10-80 .mu.m/minute.
When the composition of the present invention is applied onto a
substrate, it is possible to control layer thickness and coating
uniformity by regulating the solid concentration in the liquid
coating composition and the coated amount.
In the present invention, it is also preferable to form an
antireflection layer composed of a plurality of layers in such a
manner that the medium refractive index layer and high refractive
index layer, described below, are provided.
The configuration example of the antireflection layer usable in the
present invention is described below, however the antireflection
layer is not limited thereto.
Cellulose ester film/hard coat layer/low refractive index layer
Cellulose ester film/hard coat layer/medium refractive index
layer/low refractive index layer
Cellulose ester film/hard coat layer/high refractive index
layer/low refractive index layer
Cellulose ester film/hard coat layer/medium refractive index
layer/high refractive index layer/low refractive index layer
Cellulose ester film/antistatic layer/hard coat layer/medium
refractive index layer/high refractive index layer/low refractive
index layer
Cellulose ester film/hard coat layer/antistatic layer/medium
refractive index layer/high refractive index layer/low refractive
index layer
Antistatic layer/cellulose ester film/hard coat layer/medium
refractive index layer/high refractive index layer/low refractive
index layer
Cellulose ester film/hard coat layer/high refractive index
layer/low refractive index layer/high refractive index layer/low
refractive index layer
(Medium Refractive Index Layer and High Refractive Index Layer)
The constituting components of the medium and high refractive index
layers are not particularly limited as long as the specified
refractive index layer is prepared. However, it is preferable that
the above layer is composed of the following metal oxide particles
at a high refractive index, and binders. Other additives may be
incorporated. The refractive index of the medium refractive index
layer is preferably 1.55-1.75, while that of the high refractive
index layer is preferably 1.75-2.20. The thickness of the high and
medium refractive index layers is preferably 5 nm-1 .mu.m, is more
preferably 10 nm-0.2 .mu.m, but is most preferably 30 nm-0.1 .mu.m.
It is possible to coat those layers employing the same coating
method as that of the above low refractive index layer.
<Metal Oxide Particles>
Metal oxide particles are not particularly limited. For example,
employed as a main component may be titanium dioxide, aluminum
oxide (alumina), zirconium oxide (zirconia), zinc oxide,
antimony-doped tin oxide (ATO), antimony pentaoxide, indium-tin
oxide (ITO), and iron oxide, which may be blended. In the case of
use of titanium dioxide, in term of retardation of activity of
photocatalysts, it is preferably to employ core/shell structured
metal oxide particles which are prepared in such a manner that
titanium oxide is employed as a core and the core is covered with a
shell composed of alumina, silica, zirconia, ATO, ITO, or antimony
pentaoxide.
The refractive index of metal oxide particles is preferably
1.80-2.60, but is more preferably 1.90-2.50. The average diameter
of the primary particles of the metal oxide particles is preferably
5 nm-200 nm, but is more preferably 10-150 nm. When the particle
diameter is excessively small, metal oxide particles tend to
aggregate to degrade dispersibility, while when it is excessively
large, haze is undesirably increased. Inorganic particles are
preferably in the form of rice grain, needle, sphere, cube, or
spindle, or amorphous.
Metal oxide particles may be surface-treated with organic
compounds. Examples of such organic compounds include polyol,
alkanolamine, stearic acid, silane coupling agents, and titanate
coupling agents. Of these, most preferred are silane coupling
agents, described below. At least two types of surface treatments
may be combined.
It is possible to prepare high and medium refractive index layers
exhibiting desired refractive indices via appropriate selection of
the type of metal oxides and the addition ratio thereof.
<Binders>
Binders are incorporated to improve film forming properties and
physical properties of a coating. Employed as such binders may, for
example, be the aforesaid ionizing radiation curing type resins,
acrylamide derivatives, multifunctional acrylates, acrylic resins,
and methacrylic resins.
(Metal Compounds and Silane Coupling Agents)
Incorporated as other additives may be metal compounds and silane
coupling agents, which may be employed as a binder.
Employed as the metal compounds may be the compounds represented by
Formula (7) or chelate compounds thereof. A.sub.nMB.sub.x-n Formula
(7) wherein M represents a metal atom; A represents a hydrolysable
functional group or a hydrocarbon group having a hydrolysable
functional group; B represents a group of atoms, which covalently
or ionically bonds metal M; x represent valence of metal atom M;
and n represents an integer of not less than 2 and not more than
x.
Examples of hydrolysable functional group A include an alkoxyl
group, a halogen atom such as a chorine atom, an ester group, and
an amido group. Preferred as the compounds represented by above
Formula (4) are alkoxides having at least two alkoxyl groups
bonding a metal atom, or chelate compounds thereof. In view of
refractive index, reinforcing effects of coating strength, and ease
of handling, cited as preferred metal compounds are titanium
alkoxides, zirconium alkoxides, and silicon alkoxides, or chelate
compounds thereof. Titanium alkoxides exhibits a high reaction
rate, a high refractive index, and ease of handling. However, its
excessive addition degrades lightfastness due to its photocatalytic
action. Zirconium akloxides exhibit a high refractive index, but
tends to result in cloudiness, whereby careful dew point management
is required during coating. On the other hand, silicon alkoxides
exhibit a low reaction rate and a low refractive index, but ease of
excellent handling and excellent lightfastness. Silane coupling
agents can react with both inorganic particles and organic
polymers, whereby it is possible to prepare a strong coating.
Further, titanium aloxides enhance reaction with ultraviolet
radiation curing resins and metal alkoxides, whereby it is possible
to enhance physical characteristics of a coating even by a small
amount of their addition.
Examples of titanium alkoxides include tetramethoxytitaium,
tetraethoxytitanium, tetra-iso-propoxytitanium,
tetra-n-propoxytitanium, tetr-n-butoxytitanium,
tetra-sec-butoxytitanium, and tetra-tert-butoxytitanium.
Examples of zirconium alkoxides include tetramethoxyzirconium,
tetraethoxyzirconium, tetra-iso-propoxyzirconium,
tetra-n-proxyzirconium, tetra-n-butoxyzirconium,
tetra-sec-butoxyzirconium, and tetra-tert-butoxyzirconium.
Silicon alkoxides and silane coupling agents are the compounds
represented by following Formula (8). R.sub.mSi(OR').sub.n Formula
(8) wherein R represents a reactive group such as an alkyl group
(preferably an alkyl group having 1-10 carbon atoms), a vinyl
group, a (meth)acryloyl group, an epoxy group, an amido group, a
sulfonyl group, a hydroxyl group, a carboxyl group, or an alkoxyl
group, R' represents an alkyl group (preferably an alkyl group
having 1-10 carbon atoms), and m+n is 4.
Specifically cited are tetramethoxysilane, tetraethoxysilane,
tetra-iso-propoxysilane, tetra-n-propoxysilane,
tetra-n-butoxysilane, tetra-sec-butoxysilane,
tetra-tert-butoxysilane, terapentaethoxysilane,
methyltrimethoxysilane, methyltriethoxysilane,
methyltriproxysilane, methyltributoxysilane,
dimethyldimethoxysilane, dimethyldiethoxysilane,
hexyltrimethoxysilane, vinyltriethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, and
3-(2-aminoethylaminopropyl)trimethoxysilane.
Cited as preferred chelating agents which are allowed to coordinate
with a free metal compound to form a chelate compound may be
alkanolamines such as diethanolamine or triethanolamine; glycols
such acetylene glycol, diethylene glycol, or propylene glycol; and
acetylacetone, ethyl acetacetate, having a molecular weight of at
most 100,000. By employing such chelating agents, it is possible to
prepare chelate compounds which are stable for water mixing and
exhibit excellent coating strengthening effects.
In the medium refractive index composition, the added amount of the
metal compounds is preferably less than 5% by weight in terms of
metal oxides, while in the high refractive index composition, the
same is preferably less than 20% by weight in terms of metal
oxides.
(Polarizing Plate)
The polarizing plate of the present invention will now be
explained.
The cellulose ester film of the present invention is preferably
employed as a polarizing plate protective film provided on at least
one surface of a polarizer where the cellulose ester film of the
present invention is preferably provided the cell side surface of
the polarizer. The cellulose ester film of the present invention
may be provided on both surfaces of the polarizer.
It is possible to prepare a polarizing plate employing a common
method. It is preferable that the reverse side of the cellulose
ester film of the present invention is subjected to an alkali
saponification treatment and the resulting cellulose ester film is
adhered, employing an aqueous solution of completely-saponified
polyvinyl alcohol, onto at least one surface of a polarizer which
has been prepared by being immersed into an iodine solution
followed by stretching. Further, the above polyvinyl alcohol film
is preferably an ethnically modified polyvinyl alcohol film.
The cellulose ester film of the present invention or another
polarizing plate protective film may be employed on the other
surface of the above mentioned polarizer. Employed as a polarizing
plate protective film used on the other surface, in place of the
cellulose ester film of the present invention, may be commercially
available cellulose ester film. Examples of a preferably employable
commercially available cellulose ester film include: 8UX, 8UY, 4UX,
4UY, 5UN, and KC8UX-RHA (all produced by Konica Minolta Opto,
Inc.). By using the cellulose ester film of the present invention
in combination, obtained is a polarizing plate exhibiting excellent
visibility, excellent flatness and a stable viewing angle enlarging
effect.
(Ethylenically Modified Polyvinyl Alcohol)
In the present invention, a stretched and dyed ethylenically
modified polyvinyl alcohol is preferably used as a polarizer. More
preferable is to use an ethylenically modified polyvinyl alcohol
having an ethylene unit content of 1-4 mol %, a degree of
polymerization of 2,000 and a saponification ratio of 99.0-99.99
mol %, and specifically preferable is to use an ethylenically
modified polyvinyl alcohol film of which the hot-water cutting
temperature is 66-73.degree. C. Further, in order to decrease color
macules, it is more preferable that the difference of the hot water
cutting temperature between two points 5 cm apart in the TD
direction is at most 0.5.degree. C.
Further, in order to decrease color mucules, it is particularly
preferable that the film thickness is 5-20 .mu.m.
A polarizer employing the ethylenically modified polyvinyl alcohol
film exhibits excellent polarizing performance and
durability as well as decreases color macules and is preferably
applied in a large screen in-plane switching mode liquid crystal
display.
Employed as the ethylenically modified polyvinyl alcohol (being the
ethylenically modified PVA) may be those which are prepared in such
a manner that ethylene-vinyl ester based polymers, prepared by
copolymerizing ethylene and vinyl ester based monomers, are
saponified in which vinyl ester units are employed as vinyl alcohol
units. Examples of the above vinyl ester based monomers include
vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate,
vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivaliate, and
versatic acid vinyl esters. Of these, it is preferable to employ
vinyl acetate.
The ethylene unit content (being the copolymerized amount of
ethylene) in the ethylenically modified PVA is 1-4 mol %, however,
is preferably 1.5-3 mol % and is more preferably 2-3 mol %.
The content of the ethylene units in the above described range is
preferable since the polarizablity and the durability are improved
and color macules are reduced.
Further, the ethylenically modified polyvinyl alcohol may be
prepared by copolymerizing a monomer, for example, described below
with the vinyl ester based monomer. The content of such a monomer
is preferably not more than 15 mol % and more preferably not more
than 5 mol %.
Examples of such a copolymerizable monomer with the vinyl ester
based monomer include: olefins having 3-30 carbon atoms such as
propylene, 1-butene, or isobutene; acrylic acid and salts thereof;
acrylic acid esters such as methyl acrylate, ethyl acrylate,
n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl
acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl
acrylate, or octadecyl acrylate; methacrylic acid and salts
thereof; methacrylic acid esters such as methyl methacrylate, ethyl
methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl
acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl
methacrylate, dodecyl methacrylate, or octadecyl methacrylate;
acrylamide derivatives such as acrylamide, N-methylacrylamide,
N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide,
acrylamide propane sulfinic acid and salts thereof,
acrylamidopropyldimethylanine and salts thereof, N-methylol
acrylamide and derivatives thereof; methacrylamide derivatives such
as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide,
methacrylamidopropane sulfonic acid and salts thereof,
methacrylamidopropyldimethylamine and salts thereof, or N-methylol
methacrylamide and derivatives thereof; N-vinylamides such as
N-vinylformamide, N-vinylacetamide, or n-vinylpyrrolidone; vinyl
ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl
vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl
vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, or stearyl
vinyl ether; nitrites such as acrylonitrile or methacrylonitrile;
halogenated vinyls such as vinyl chloride, vinylidene chloride,
vinyl fluoride, or vinylidene fluoride; allyl compounds such as
allyl acetate or allyl chloride; maleic acid, and salts and esters
thereof; itaconic acid, and salts and esters thereof; vinylsilyl
compounds such as vinylmethoxysilane; and N-vinylamides such as
isopropenyl acetate, N-vinylformamide, N-vinylacetamide, or
N-vinylpyrrolidone.
The degree of polymerization of ethylenically modified PVA is
2,000, preferably 2,500, and more preferably 2,000 in terms of
polarizing performance and durability. When the degree of
polymerization of ethylenically modified PVA is less than 2,000,
the polarizing performance and durability of the polarizer are
undesirably degraded. The degree of polymerization of 4,000 or less
is preferred since color macules of the polarizer tend not to
occur.
The degree of polymerization of the ethylenically modified PVA is a
weight average polymerization degree determined by means of GPC
(Gel Permeation Chromatography). This weight average polymerization
degree is a value obtained by performing GPC measurement at
40.degree. C. employing hexafluoroisopropanol (HFIP) added with 20
millimol/liter of sodium trifluoroacetate as the mobile phase using
monodispersed PMMA as a standard.
In view of polarization performance and durability of the
polarizer, the ratio of saponification of the ethylenically
modified PVA constituting the polarizer is preferably 99.0-99.99
mol %, is more preferably 99.9-99.99 mol %, but is most preferably
99.95-99.99 mol %.
The method to produce an ethylenically modified PVA film is not
specifically limited, however, preferable are a casting method and
a melt extrusion method, in order to obtain a preferable
ethylenically modified PVA film. The obtained ethylenically
modified PVA film is dried and is subjected to a thermal treatment,
if necessary.
Cited as solvents to dissolve the ethylenically modified PVA
employed during production of ethylenically modified PVA film may,
for example, be dimethylsulfoxide, dimethylformamide,
dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin,
propylene glycol, triethylene glycol, tetraethylene glycol,
trimethylolpropane, ethylenediamine, diethylenetriamine, and water.
These may be employed individually or in combination of at least
two types. Of these, suitably employed is dimethylsulfoxide and
water, or a mixed solvent of glycerin and water.
The ratio of ethylenically modified PVA, incorporated in an
ethylenically modified PVA solution or water-containing
ethylenically modified PVA employed during production of the
ethylenically modified film, varies depending on the degree of
polymerization of the ethylenically modified PVA, but is commonly
20-70% by weight, is preferably 25-60% by weight, but is more
preferably appropriately 30-55% by weight, but is most preferably
35-50 by weight. When the ratio of the ethylenically modified PVA
exceeds 70% by weight, viscosity of the ethylenically modified PVA
solution or the water-containing ethylenically modified PVA becomes
excessively high, whereby it becomes difficult to prepare a film
without foreign matter and defects due to difficult filtration and
defoaming. On the other hand, when the ratio of the ethylenically
modified PVA is at most 20% by weight, the viscosity of the
ethylenically modified PVA solution or the water-containing
ethylenically modified PVA becomes excessively low, whereby it
becomes difficult to prepare a PVA film at the targeted thickness.
Further, if desired, plasticizers, surface active agents, and
dichroic dyes may be incorporated in the above ethylenically
modified PVA solution or water-containing ethylenically modified
PVA.
During production of the ethylenically modified PVA film, it is
preferable to incorporate polyhydric alcohols as a plasticizer.
Examples of polyhydric alcohols include ethylene glycol, glycerin,
propylene glycol, diethylene glycol, diglycerin, triethylene
glycol, tetraethylene glycol, and trimethylolpropane. These may be
employed individually or in combinations of at least two types. Of
these, in view of orientation enhancement effects, diglycerin,
ethylene glycol, and glycerin are preferable.
The added amount of polyhydric alcohols is preferably 1-30 parts by
weight with respect to 100 parts by weight of the ethylenically
modified PVA, is more preferably 3-25 parts by weight, but is most
preferably 5-20 parts by weight. When the added amount is at most 1
part by weight, dying properties and orientation properties are
occasionally degraded, while when it exceeds 30 parts by weight,
the ethylenically modified film becomes excessively flexible,
whereby handling properties tend to be degraded.
During production of the ethylenically modified PVA film, it is
preferable to incorporate surface active agents. The types of
surface active agents are not particularly limited, but nonionic or
cationic surface active agents are preferred. Examples of suitable
anionic surface active agents include carboxylic acid types such as
potassium laurate, sulfuric acid ester types such as octyl sulfate,
and sulfonic acid types such as dodecylbenznene sulfonate. Examples
of suitable nonionic surface active agents include alkyl ether
types such as polyoxyethylene oleyl ether; alkyl phenyl ether types
such as polyoxyethylene octyl phenyl ether; alkyl ester types such
as polyoxyethylenelaurate; alkylamine types such as polyoxyethylene
lauryl aminoether; alkylamide types such as polyoxyethylene lauric
acid amide; polypropylene glycol ether types such as
polyoxyethylene polyoxypropylene ether; alkanol amide types such as
oleic acid diethanolamide; and allyl phenyl ether types such as
polyoxyalkylene phenyl ether. These surface active agents may be
employed individually or in combinations of at least two types.
The added amount of surface active agents is preferably 0.01-1 part
by weight with respect to 100 parts by weight of the ethylenically
modified PVA and is more preferably 0.02-0.5 part by weight. When
the added amount is at most 0.01 part by weight, effects to improve
film casting properties and peeling properties are hardly
exhibited, while when it exceeds 1 part by weight, surface active
agents are dissolved out onto the surface of the ethylenically
modified PVA film to result in blocking, whereby handling
properties tend to be degraded.
The thickness of the ethylenically modified PVA film employed to
prepare a polarizer is preferably 10-50 .mu.m, but is more
preferably 20-40 .mu.m. When the thickness is at most 10 .mu.m,
uniform stretching is hardly performed due to excessively low film
strength, whereby color macules of the polarizer tend to be
generated. On the other hand, when the thickness exceeds 50 .mu.m,
during production of a polarizer via uniaxial orientation of the
ethylenically modified PVA film, the thickness tends to vary due to
neck-in at the ends, whereby color macules of the polarizer tend to
be undesirably enhanced.
Further, to produce a polarizer employing an ethylenically modified
PVA film, for example, the ethylenically modified PVA film may be
dyed, uniaxially stretched, fixed and dried, if desired, thermally
treated. The order of the dying, uniaxial stretching, and fixing is
not particularly limited. Further, the uniaxial stretching may be
repeated twice or more.
Dying may be performed at any time such as prior to uniaxial
stretching, during uniaxial stretching, or after uniaxial
stretching. Employed as dyes for dying are dichroic dyes. These may
be employed singly or in combinations of at least two types. Dying
is commonly performed by immersing a PVA film into a solution
incorporating the above dyes. Alternatively, the above dyes may be
blended into a PVA film during casting. The above dying conditions
and methods are not particularly limited.
It is possible to conduct uniaxial stretching employing either a
wet stretching method or a dry heat stretching method, and in
heated water (a solution incorporating the above dyes or the fixing
bath, described below, may be employed) or in an atmosphere
employing the ethylenically modified PVA film after water
absorption. The temperature during stretching is not particularly
limited. When the ethylenically modified PVA film is stretched in
heated water (being wet system stretching), the stretching
temperature is preferably 30-90.degree. C., while in the case of
dry heat stretching, it is preferably 50-180.degree. C. The
stretching factor (the total stretching factor in the case of
multistage uniaxial stretching) is preferably at least 4 in terms
of polarization performance of a polarizing film, but is most
preferably at least 5. The upper limit of the stretching factor is
not particularly limited. However, the stretching factor is
preferably at least 8, since uniform stretching is readily
performed. The film thickness after stretching is preferably 2-20
.mu.m, but is more preferably 5-15 .mu.m.
To strengthen adsorption of the above dyes onto the ethylenically
modified PVA film, a fixing treatment is frequently conducted.
Commonly, boric acid and/or boron compounds are added to a
treatment bath employed for the fixing treatment. Alternatively, if
desired, iodine compounds may be incorporated in the treatment
bath.
Drying of a prepared polarizer is preferably performed between
30-150.degree. C., but is more preferably performed between
50-150.degree. C.
An polarizing plate protective layer is adhered to one surface or
both surfaces of the polarizer, whereby a polarizing plate is
prepared. Listed as adhesives for the above adhesion may be a PVA
based adhesive and an urethane based adhesive. Of these, the PVA
based adhesive is preferable.
The polarizing film as a major constituent of the polarizing plate
is an element that permits passage of only the light in one
polarizing plane. The currently known typical polarizing film is a
polyvinyl alcohol based polarizing film. The polyvinyl alcohol
based film dyed by iodine and that dyed by dichromatic dyes are
available. The polarizing film to be used is produced as follows:
The aqueous solution of polyvinyl alcohol is used to form a film,
which is dyed and is uniaxially stretched. Alternatively, the film
is uniaxially stretched and then dyed. Thus obtained polarizing
film is preferably subjected to durability treatment using a boric
acid compound. The cellulose ester film of the present invention is
adhered on a surface of the polarizing film to form a polarizing
plate. The adhesion is preferably carried out using an aqueous
adhesive containing, for example, a fully-saponified polyvinyl
alcohol as a main component.
The polarizing plate using a conventional cellulose ester film was
lacking in flatness and wavy unevenness was observed in a reflected
image. The wavy unevenness increased when the polarizing plate was
subjected to a durability test under a condition of 60.degree. C.
and 90% RH. On the contrary, the polarizing plate using a cellulose
ester film of the present invention showed excellent flatness and
wavy unevenness did not increase even after a durability test under
a condition of 60.degree. C. and 90% RH.
The polarizing plate employing the cellulose ester film of the
present invention was found to be excellent in flexibility and
formed less cutting scrap when the film was cut, resulting in
reducing defect due to the cutting scrap and being excellent for
manufacturing.
(Liquid Crystal Display)
By mounting the polarizing plate of the present invention on a
display device, it is possible to prepare various types of liquid
crystal display of the present invention exhibiting excellent
visibility. The cellulose ester film of the present invention is
preferably employed in a reflection LCD, a transmissive LCD, or
semi-transmissive LCD, as well as in various driving mode LCDs such
as a TN mode LCD, an STN mode LCD, an OCB mode LCD, an HAN mode
LCD, a VA mode LCD (including a PVA mode LCD and an MVA mode LCD),
or an IPS mode LCD, however, specifically preferable is to be used
in an in-plane switching mode LCD such as an IPS mode LCD or a FFS
mode LCD. Further, in a large screen liquid crystal display of 17
size or more, or specifically 30 size or more, in addition to the
effect of the present invention, an effect of preventing eye
fatigue even after a long time observation was obtained, since no
distortion was observed in the image reflected by the screen, which
was just like an image reflected by a mirror surface, while
distortion had been observed in the image of a fluorescent lamp
reflected by a conventional LCD screen due to color unevenness or
wavy unevenness.
EXAMPLES
The present invention is described below referring examples but the
present invention is not limited to the examples. "Percent" in the
examples is "percent by weight" as long as any specific description
is not attached.
Example
(Synthesis of Acryl Polymer)
Cluster polymerization was carried out according to the
polymerization method described in JP-A No. 2000-344823. In a flask
having a stirrer, a nitrogen gas inlet tube, a thermometer, an
opening for putting in material and a reflux condenser, the
following methyl methacrylate and ruthenocene were introduced while
heating the content of the flask at 70.degree. C. After that, a
half of the following .beta.-mercaptopropionic acid which was
sufficiently subjected to gas replacing treatment by nitrogen gas
was added into the flask while stirring. After adding the
.beta.-mercaptopropionic acid, the content of the flask was stirred
at 70.degree. C. for 2 hours for carrying out polymerization. Then
the remaining half of the .beta.-mercaptopropionic acid atmosphere
being substituted with nitrogen gas was further added and the
temperature was kept at 70.degree. C. for continuing the
polymerization for 4 hours while stirring. Then the temperature of
the reaction product was cooled to ambient temperature and 20 parts
by weight of a 5 weight % tetrahydrofuran solution of benzoquinone
for stopping the polymerization. The polymerized product was
gradually heated to 80.degree. C. under reduced pressure in an
evaporator for removing tetrahydrofuran, remaining monomer and
remaining thiol compound. Thus Acryl Polymer H5 was obtained. The
weight average molecular weight of the polymer was 1,000.
(Preparation of Polyester K1)
In a three necked flask, a stirrer, a nitrogen gas inlet tube, a
thermometer and a water remover tube were mounted. The water
remover tube had a fractional tube. At the end of the fractional
tube, a condenser tube having a thermometer on the top was
equipped. A water receiver having a scale (m1) was provided beneath
the condenser, the water receiver also having a exhaust tube on the
top. In the flask, 186 g of ethylene glycol and 236 g of succinic
acid were charged and the inside of the flask was heated to 80 to
90.degree. C. while slowly passing nitrogen gas and then stirring
was started. The temperature was increased to 150-160.degree. C.
over 1 hour while keeping the temperature of the top of the
condenser at 100.degree. C. or less in order to remove only water
and not to let glycol out. Then the temperature was increased to
190-200.degree. C. until 72 g water came out and then the inside
temperature was lowered to 110-120.degree. C. After adding 120 g of
acetic acid, the temperature was increased again to 150-160.degree.
C. When 36 g of water was further came out, the inside temperature
was lowered to 110-120.degree. C. subsequently to 80.degree. C. The
reaction product was deposited using acetone and separated by
filtering to obtain polyester K1. The weight average molecular
weight of K1 was determined to be 434 by means of GPC.
(Polymerization of K2 to 11)
Each of K2 to 11 was prepared according to the same manner as K1: a
combination of a dihydric alcohol and a dibasic carboxylic acid
shown in Table 1-Table 2 was charged and heated while stirring.
After water came out, the temperature was lowered to add a
monoalcohol or a monocarboxylic acid listed in Table 1-Table 2, and
the temperature was increased again while stirring. After water
further came out, the inside temperature was lowered and the
reaction product was deposited using acetone followed by separation
by filtering. Thus K2 to 11 were obtained. The molecular weight of
the product was controlled by varying the amount of water came out.
For K5 and K7, the each mixing ratio of two kinds of alcohols to
two kinds of carboxylic acids was set to 1:1. The weight average
molecular weights of the obtained polymers are shown below. The
figures in the parentheses represent the weight average molecular
weights: K2(800), K3(234), K4(3000), K5(6000), K6(10000),
K7(11000), K8(234), K9(1000), K10(8000), K11(10000).
(Polymerization of H4)
H4 was prepared in the same manner as K1-K11 except that the
reaction was stopped after first water came out. The product was
deposited by acetone. The weight average molecular weight was
800.
TABLE-US-00001 Methyl methacrylate 100 parts by weight Ruthenocene
(metallic catalyst) 0.05 parts by weight .beta.-mercaptopropionic
acid 12 parts by weight
Besides, Acryl Polymers AC 1 through 8 were synthesized by
referring the method described in JP-A No. 2003-12859.
(Preparation of Cellulose Ester Film 1)
TABLE-US-00002 (Dope composition) Cellulose triacetate S1 (acetyl
substitution 100 parts by weight degree 0.46, propionyl
substitution degree 2.52) 2-(2'-hydroxy-3',5'-di-t-butylphenyl) 2
parts by weight benzotriazole K1 (a kind of compound represented by
30 parts by weight Formula (1) wherein B.sub.1 represents a
monocarboxylic acid having 1 - 12 carbon atoms, G represents a
dihydric alcohol having 2 - 12 (carbon atoms and A represents a
dibasic acid having 2 - 12 carbon atoms) Methylene chloride 475
parts by weight Ethanol 50 parts by weight
The dope composition was put into a closed vessel and heated by
70.degree. C. and the cellulose triacetate was completely dissolved
by stirring to form a dope. The time for dissolving was 4 hours.
The dope composition was filtered and uniformly cast on a stainless
steel band support of 22.degree. C. at a dope temperature of
35.degree. C. using a belt casting apparatus.
The cast dope was dried into the peelable range and peeled off from
the stainless band support. The amount of remaining solvent in the
dope was 25% at this time. The time necessary from the dope casting
to the peeling was 3 minutes. After peeling from the stainless
steel band support, the film was dried at 120.degree. C. while
stretching by 1.01 times in the width direction by a tenter. After
that the film was released from the width holding and dried at
120.degree. C. while conveying many rollers and further dried in a
drying zone at 135.degree. C. for finishing the drying. A knurling
treatment with a width of 10 mm and height of 5 .mu.m was applied
on the both edges of the film. Thus cellulose ester film having a
thickness of 40 .mu.m was prepared. The width and length of the
film were 1,300 mm and 3,000 m, respectively. The initial and final
winding up tensions were 150 N/1,300 mm and 100 N/1,300 mm,
respectively.
(Preparation of Cellulose Ester Films 2 through 37)
Cellulose Ester Films 2 through 37 were prepared in the same manner
as Cellulose Ester Film 1 except that K1 and its adding amount were
changed to the polyester and the amount thereof listed in Table 5
and the acryl polymer listed in Table 5 was added to a part of the
films and the thickness was changed as listed in Table 5. In Table
5, AC1 to AC8 are described in Table 3 and H1 to H5 are described
in Table 4.
(Preparation of Cellulose Ester Films 38 and 39)
Cellulose Ester Films 38 and 39 were prepared in the same manner as
Cellulose Ester Film 1 except that S2 (acetyl substitution degree
of 1.9 and propionyl substitution degree of 1.0) and S3 (acetyl
substitution degree of 1.9 and propionyl substitution degree of
1.08), respectively, were used instead of S1.
TABLE-US-00003 TABLE 1 B.sub.1-(G-A).sub.mG-B.sub.1 Com- pound No.
B.sub.1 G A Mw K1 CH.sub.3COO C.sub.2H.sub.4--O
CO--C.sub.2H.sub.4--COO 434 K2 CH.sub.3COO C.sub.2H.sub.4--O
CO--C.sub.2H.sub.4--COO 800 K3 HCOO C.sub.2H.sub.4--O CO--COO 234
K4 C.sub.7H.sub.15COO C.sub.2H.sub.4--O CO--C.sub.2H.sub.4--COO
3000 K5 CH.sub.3COO C.sub.2H.sub.4--O.sup.1)
CO--C.sub.2H.sub.4--COO.sup.2) 600- 0 C.sub.4H.sub.8--O.sup.1)
CO--C.sub.4H.sub.8--COO.sup.2) K6 C.sub.11H.sub.23COO
C.sub.12H.sub.24--O CO--C.sub.10H.sub.20--COO 10000- K7
C.sub.11H.sub.23COO C.sub.2H.sub.4--O.sup.3)
CO--C.sub.2H.sub.4--COO.su- p.4) 11000 C.sub.12H.sub.24--O.sup.3)
CO--C.sub.10H.sub.20--COO.sup.4) .sup.1) 4)Mixing Ratio 1:1
TABLE-US-00004 TABLE 2 B.sub.2-(A-G).sub.nA-B.sub.2 Compound No.
B.sub.2 A G Mw K8 CH.sub.3O CO--COO C.sub.2H.sub.4--O 234 K9
C.sub.2H.sub.5O CO--C.sub.2H.sub.4--COO C.sub.2H.sub.4--O 1000 K10
C.sub.2H.sub.5O CO--COO C.sub.4H.sub.8--O 8000 K11 C.sub.2H.sub.5O
CO--COO C.sub.2H.sub.4--O 10000
TABLE-US-00005 TABLE 3 (HEA).sub.X-(MMA).sub.Y Compound No. X Y Mw
AC1 1 99 3000 AC2 5 95 4000 AC3 10 90 8000 AC4 20 80 12000 AC5 40
60 18000 AC6 50 50 20000 AC7 40 60 18000 AC8 50 50 20000
TABLE-US-00006 TABLE 4 Compound No. B.sub.1 G A Mw
B.sub.1-(G-A).sub.mG-B.sub.1 H1 CH.sub.3COO p-C.sub.6H.sub.4--O
CO--C.sub.2H.sub.4--COO 800 H2 CH.sub.3COO C.sub.2H.sub.4--O
CO--C.sub.6H.sub.4--COO 800 H3 C.sub.6H.sub.5COO C.sub.2H.sub.4--O
CO--C.sub.2H.sub.4--COO 800 H4 OH C.sub.2H.sub.4--O
CO--C.sub.2H.sub.4--COO 800 Acryl Polymer H5 PMMA 1000 MMA: Methyl
methacrylate HEA: 2-hydroxyethyl acrylate
TABLE-US-00007 TABLE 5 Cellulose Polyester Acryl polymer Thickness
*1 triacetate Compound *2 Compound *2 (.mu.m) Flatness Rt (nm) Ro
(nm) 1 S1 K3 30 -- -- 40 A -20 2 2 S1 K1 20 -- -- 40 A -10 1 3 S1
K1 15 -- -- 40 A -5 0 4 S1 K1 15 -- -- 80 A -5 0 5 S1 K2 10 -- --
40 A 0 0 6 S1 K4 10 -- -- 50 A 0 0 7 S1 K5 10 -- -- 40 A 0 0 8 S1
K6 5 -- -- 40 A 5 0 9 S1 K7 5 -- -- 40 A 5 0 10 S1 K8 15 -- -- 40 A
-5 0 11 S1 K9 15 -- -- 80 A -5 0 12 S1 K10 15 -- -- 80 A -5 0 13 S1
K11 10 -- -- 20 B 0 0 14 S1 K11 10 -- -- 40 A 0 0 15 S1 K11 10 --
-- 80 A 0 0 16 S1 K1 10 AC1 10 40 A -10 1 17 S1 K1 10 AC2 1 50 A 0
0 18 S1 K1 15 AC3 5 40 A -10 1 19 S1 K1 5 AC3 20 40 A -15 2 20 S1
K1 10 AC4 10 40 A -10 1 21 S1 K1 5 AC4 15 40 A -10 1 22 S1 K1 10
AC5 10 40 A -10 1 23 S1 K1 2 AC6 10 80 A 5 0 24 S1 K1 10 AC7 10 40
A -10 1 25 S1 K1 10 AC8 10 40 A -10 1 26 S1 H1 20 -- -- 80 D 25 5
27 S1 H2 20 -- -- 80 D 25 5 28 S1 H3 20 -- -- 80 D 30 5 29 S1 H5 10
-- -- 40 A 0 0 30 S1 H5 20 -- -- 80 A -5 0 31 S1 K1 15 -- -- 40 A
-5 0 32 S1 K1 15 -- -- 80 A -5 0 33 S1 K1 10 AC4 10 40 A -10 1 34
S1 H5 10 -- -- 40 A 0 0 35 S1 K1 15 -- -- 80 A -5 0 36 S1 H4 20 --
-- 80 B -5 1 37 S1 H4 10 -- -- 80 B 5 0 38 S2 K1 15 -- -- 80 A -10
1 39 S3 K1 15 -- -- 80 A -7 1 *1: Cellulose ester film No., *2:
(Weight %)
(Preparation of Polarizer 1)
One hundred parts by weight of ethylenically modified polyvinyl
alcohol having an ethylene content of 2.1 mol %, a saponification
degree of 99.92 mol % and a polymerization degree of 3,000, was
impregnated with 10 parts by weight of glycerin, and 200 parts by
weight of water, and was molten, kneaded and defoamed, and then
extruded through a T-die onto a metal roll and dried. Thus an
ethylenically modified polyvinyl alcohol film having a thickness of
40 .mu.m was obtained.
The obtained ethylenically modified polyvinyl alcohol film was
subjected to treatments for preliminary swelling, dyeing, uniaxial
stretching, fixing, drying and heating in this order to prepare
Polarizer 1. Namely, the ethylenically modified polyvinyl alcohol
film was immersed in water of 30.degree. C. for 60 minutes for
preliminary swelling, and immersed for 2 minutes in a 35.degree. C.
aqueous solution of 40 g/liter of boric acid, 0.4 g/liter of iodine
and 60 g/liter of potassium iodide. Then the film was uniaxially
stretched in a 4% boric acid aqueous solution of 55.degree. C.; the
stretching ratio was varied so that the film thickness became to 5
to 25 .mu.m. After that the film was subjected to a fixing
treatment by immersing for 5 minutes into a 30.degree. C. aqueous
solution of 60 g/liter of potassium iodide, 40 g/liter of boric
acid and 10 g/liter of zinc chloride. The film was taken out and
dried by 40.degree. C. hot air at ordinary humidity and thermally
treated for 5 minutes at 100.degree. C.
The transmittance and polarization degree of thus obtained
Polarizer were 43% and 99.9%, respectively.
(Preparation of Polarizer 2)
A polyvinyl alcohol film having a thickness of 120 .mu.m was
immersed in 100 parts by weight of an aqueous solution containing 1
part by weight of iodine and 4 parts by weight of boric acid and
uniaxially stretched at 50.degree. C. to prepare Polarizer 2. The
stretching ratio was varied so that the film thickness became 20 to
25 .mu.m.
(Polarizing Plates 1-30 and 36-39)
Cellulose Ester Films 1-30 each were treated with 2.5 mol/liter
aqueous solution of sodium hydroxide at 40.degree. C. for 60
seconds and washed by water for 3 minutes for forming a saponified
layer. Each of the alkali-treated films was pasted on both sides of
the above prepared Polarizer 1 by an adhesive of 5% aqueous
solution of completely saponified polyvinyl alcohol. Thus
Polarizing Plates 1-30 and 36-39 were prepared from Cellulose Ester
Films 1-30 and 36-39, respectively.
(Preparation of Polarizing Plates 31 through 34)
Cellulose Ester Films 31-34 were each treated by 2.5 mol/liter
aqueous solution of sodium hydroxide of 40.degree. C. for 60
seconds and washed by water for 3 minutes for forming a saponified
layer. Each of the alkali-treated films was pasted on both sides of
the above prepared Polarizer 2 by an adhesive of 5% aqueous
solution of completely saponified polyvinyl alcohol. Thus
Polarizing plate 31 through 34 were prepared from Cellulose Ester
Films 31 through 34, respectively.
(Preparation of Polarizing Plate 35)
The above Cellulose Ester Film 4 and KC8UX-RHA, manufactured by
Konica Minolta Opto Inc., were each alkali-treated for 60 seconds
at 40.degree. C. by a 5 moles/liter sodium hydroxide aqueous
solution to form a saponified layer. The alkali-treated films were
each pasted on both sides of the above prepared Polarizer 1 by an
adhesive of 5% aqueous solution of completely saponified polyvinyl
alcohol to prepare Polarizing plate 35.
[Evaluation]
Thus obtained Cellulose Ester Films 1-39 were subjected to the
following evaluation.
(Flatness)
Each of the samples was cut into a size of 90 cm.times.100 cm, and
placed on a test table over which five 50 W fluorescent lamps were
arranged in parallel so that the sample was illuminated from an
angle of 45.degree. by the fluorescent lamps, and the shape of the
image of the lamps reflected by the film surface was visually
observed and judged according to the followings criteria. The
buckling and wrinkling can be evaluated by such the method.
A: The reflected images of the 5 fluorescent lamps were
straight.
B: Some portions of the reflected images of the lamps were slightly
waved.
C: Whole reflected images of the lamps were slightly waved.
D: The reflected images of the lamps were largely waved.
(Measurements of Ro and Rt)
The average refractive index of each of the cellulose ester films
was measured by Abbe's refractometer (4T). The thickness of each of
the films was measured by a micrometer available on the market.
The retardation of the film stood for 24 hours in the environment
of 23.degree. C. and 55% RH was measured at a wavelength of 590 nm
by an automatic birefringence analyzer "KOBRA-21ADH, manufactured
by Oji Scientific Instruments, in the same environment. The above
measured average refractive index and the thickness were input to
the following expressions for obtaining the in-plane retardation Ro
and retardation in the thickness direction Rt.
Ro=(n.sub.x-n.sub.y).times.d Expression I
Rt={(n.sub.x+n.sub.y)/2-n.sub.z}.times.d Expression ii In the
expressions, n.sub.x, n.sub.y and n.sub.z each represent a
refractive index in the direction of the main axes x, y and z of
the refractive index ellipsoid, respectively, and n.sub.x and
n.sub.y are in-plane refractive indexes and n.sub.z is a refractive
index in the thickness direction. The relationship
n.sub.x.gtoreq.n.sub.y is satisfied and d is the thickness (nm) of
the film.
(Stability of Rt)
Rt of the cellulose ester film was measured after treating the film
for 10 hours at 23.degree. C. and 80% RH and the measurement of Rt
was repeated after further treating the film for 10 hours at
23.degree. C. and 20% RH. The results of the test were classified
into 4 ranks according to the following criteria.
.DELTA.Rt (nm)=Rt (23.degree. C. and 80% RH)-Rt (23.degree. C. and
20% RH)
A: .DELTA.Rt was less than 10 nm.
B: .DELTA.Rt was 10 nm or more but less than 15 nm
C: .DELTA.Rt was 15 nm or more but less than 20 nm
D: .DELTA.Rt was not less than 20 nm
Next, Polarizing plates 1 through 39-were evaluated as follows.
(Degradation of Polarizing Plate)
Each of the above prepared polarizing plates were treated for 120
hours at 80.degree. C. and 90% RH and the transmittance of each
plate was measured before and after the treatment and the results
were evaluated in 5 ranks according to the following criteria.
Difference of transmittance .DELTA.T=Td(transmittance after the
high temperature-high humidity treatment)-T0 (transmittance before
the high temperature-high humidity treatment)
A: .DELTA.T was less than 1%
B: .DELTA.T was 1% or more but less than 5%.
C: .DELTA.T was 5% or more but less than 10%.
D: .DELTA.T was 10% or more but less than 15%.
E: .DELTA.T was not less than 15%.
(Dimensional Variation of Polarizing Plate)
On each prepared polarizing plate, two markers (crosses) were drawn
along the absorbing axis of the polarizer and the polarizing plate
was treated at 80.degree. C. under 90% RH for 120 hours. The
distance between the two markers (crosses) was measured before and
after the treatment using an optical microscope. Evaluation was
carried in 5 ranks according to the following criteria. Rate of
change(%)=[(a1-a2)/a1].times.100 a1: the distance before the
treatment a2: the distance after the treatment
A: The rate of change was less than 0.1%
B: The rate of change was 0.1% or more but less than 0.5%
C: The rate of change was 0.5% or more but less than 1.0%
D: The rate of change was 1.0% or more but less than 1.5%
E: The rate of change was 1.5% or more but less than 2.0%
F: The rate of change was 2.0% or more but less than 3.0%
G: The rate of change was 3.0%-5.0% or more
(Viewing Angle Variation)
(Preparation of Liquid Crystal Display)
A crystal liquid panel for measuring the viewing angle was prepared
as follows and the properties thereof were evaluated.
The polarizing plate previously pasted on the front side (or the
viewer side) of a 32-type display W32-L7000, manufactured by
Hitachi Seisakusho Co., Ltd., was peeled off and each of Polarizing
plates 1-34 was pasted onto the glass surface of the liquid crystal
cell. The polarizing plate was pasted so that the absorbing axis of
the polarizing plate lay in the same direction as the absorbing
axis direction of the previously pasted polarizing plate. Thus
Liquid Crystal Displays 1-34 and 36-39 were prepared.
Regarding Polarizing plate 35, Liquid Crystal Display 35 was
prepared by pasting the polarizing plate so that the cellulose
ester film of the present invention faced the liquid crystal cell
and the absorbing axis of the polarizing plate lay in the same
direction as the absorbing axis direction of the previously pasted
polarizing plate.
The Liquid Crystal Displays 1 through 39 prepared as above were
subjected to the following evaluation.
The viewing angle of each of the liquid crystal displays was
measured by EZ-Contrast 160D, manufactured by ELDIM Co., Ltd., in
an environment of 23.degree. C. and 35% RH. After that, the
polarizing plates were treated for 500 hours at 60.degree. C. and
90% RH, and the viewing angle of each of the liquid crystal
displays was measured in the same manner as above. Further, the
polarizing plates were treated for 1,000 hours at at 60.degree. C.
and 90% RH, and the viewing angles thereof were measured in the
same manner as above. The evaluation was carried out in four ranks
according to the following criteria.
A: No variation in the viewing angle was observed.
B: Variation in the viewing angle was slightly observed.
C: Variation in the viewing angle was observed.
D: Considerable variation in the viewing angle was observed.
(CM (Corner Unevenness))
Liquid Crystal Displays 1-39 were prepared by pasting the
polarizing plate in the same manner as described in the evaluation
of viewing angle variation. Liquid Crystal Displays 1-39 were
treated for 300 hours at 60.degree. C. and then the condition was
restored to 23.degree. C. and 55% RH. Power switch was turned on
for lighting the backlight and a black image was displayed. After 2
hours of that, the light leaking through the black image was
visually observed and evaluated according to the following
norms.
A: No light leaking was observed at all.
B: Weak light leaking was observed at one or two points.
C: Strong light leaking was observed at one or two points.
D: Strong light leaking was observed at three or more points.
The above results were summarized in Table 6.
TABLE-US-00008 TABLE 6 Polarizer Polarizing plate Viewing Angle
Polarizing Layer Dimensional CM (Corner Variation plate No. Kind
thickness (.mu.m) Degradation variation unevenness) (500 h) (1000
h) Remarks 1 *1 20 B C B A C Inv. 2 *1 20 B C B A C Inv. 3 *1 25 A
C B A C Inv. 4 *1 20 A C B A C Inv. 5 *1 20 A C B A C Inv. 6 *1 20
A C B A C Inv. 7 *1 20 A C B A C Inv. 8 *1 10 A C B A C Inv. 9 *1 5
A C B A C Inv. 10 *1 20 A C B A C Inv. 11 *1 20 A C B A C Inv. 12
*1 20 A C B A C Inv. 13 *1 20 A C B A C Inv. 14 *1 20 A C B A C
Inv. 15 *1 20 A C B A C Inv. 16 *1 20 A A B A A Inv.. 17 *1 20 A A
B A A Inv. 18 *1 20 A A B A A Inv. 19 *1 15 A A B A A Inv. 20 *1 10
A A B A A Inv. 21 *1 20 A A B A A Inv. 22 *1 5 A A B A A Inv. 23 *1
20 A A B A A Inv. 24 *1 20 B B B A B Inv. 25 *1 20 B B B A B Inv.
26 *1 25 C G D D D Comp. 27 *1 20 C G D D D Comp. 28 *1 20 C G D D
D Comp. 29 *1 5 D E D D D Comp. 30 *1 20 E E D D D Comp. 31 *2 20 B
D B B C Inv. 32 *2 20 B D B B C Inv. 33 *2 20 B B B A B Inv. 34 *2
25 D C B D D Comp. 35 *1 20 A C B A C Inv. 36 *1 20 D D B D D Comp.
37 *1 20 C E B C D Comp. 38 *1 20 A C B A C Inv. 39 *1 20 A C B A C
Inv. *1: Polarizer 1, *2: Polarizer 2 Inv.: Inventive, Comp.:
Comparative
It is understood from Table 6 that the cellulose ester film of the
present invention is excellent in the dimensional stability, corner
unevenness (light leakage) and flatness, and gives high retardation
stability while humidity is varied, and the polarizing plate and
the IPS mode display exhibit high viewing angle stability.
* * * * *